Jerry and Carol C. Baskin University of Kentucky, Lexington. USA.
H
ere for the first time is a complete guide to the collection, processing and storage of seeds collected in the wild. Written by some of the world’s leading practitioners in the field of seed biology and conservation, this book describes procedures and protocols that are of international standard and apply to users throughout the world.
Australian Seeds provides an invaluable guide for those involved in flora conservation work. It will enable users to collect, process and store seed more efficiently, thus reducing loss of seed viability during the storage process, with potentially huge savings in time, effort and expense in the rehabilitation and restoration industries. Editors Luke Sweedman is Curator for the Western Australian Seed Technology Centre at Kings Park, Perth. He is an expert in the storage of species for both local and international threatened flora programs and provides material for display for the Kings Park Botanic Gardens. David Merritt is a Research Scientist at the Botanic Gardens and Parks Authority and The University of Western Australia. He has worked with native seeds since 1997 and his research interests include seed storage and dormancy, and the use of seeds in restoration.
Editors: L. Sweedman and D. Merritt
Australian Seeds also includes the most comprehensive pictorial guide to Australian seeds available. It features photographs of 1260 Australian species, showing clearly their size and shape. This allows collectors to determine if their collections are of good, well-shaped seed – important to prevent unnecessary time being wasted in cleaning, storing and sowing of poor quality seed.
Australian Seeds
Australian Seeds is an excellent contribution to plant conservation and restoration in Australia, and the editors and all the contributors are to be congratulated for making the information available in a single volume … it will be greatly appreciated and enjoyed by people who are fascinated by the beauty and diversity of seeds.
Australian Seeds A Guide to their Collection, Identification and Biology
Editors: Luke Sweedman and David Merritt
AUSTRALIAN
SEEDS
A GUIDE TO THEIR COLLECTION, IDENTIFICATION AND BIOLOGY
This book is dedicated to my favourite person in the world, my beautiful daughter Koromiko who has been with me throughout this entire project and who will be relieved not to hear about it again. Luke Sweedman
AUSTRALIAN
SEEDS
A GUIDE TO THEIR COLLECTION, IDENTIFICATION AND BIOLOGY
Editors: Luke Sweedman and David Merritt
© 2006 Botanic Gardens and Parks Authority of Western Australia All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests. National Library of Australia Cataloguing-in-Publication entry Australian seeds : a guide to their collection, identification and biology. Bibliography. Includes index. ISBN 0 643 09132 7 (hbk.). ISBN 0 643 09298 6 (pbk.). 1. Seeds – Australia – Identification. 2. Seeds – Collection and preservation - Australia. 3. Seeds – Processing – Australia. 4. Seeds – Storage – Australia. I. Sweedman, Luke, 1958–. II. Merritt, David J., 1975–. 631.5230994 Available from CSIRO PUBLISHING 150 Oxford Street (PO Box 1139) Collingwood VIC 3066 Australia Telephone: Local call: Fax: Email: Web site:
+61 3 9662 7666 1300 788 000 (Australia only) +61 3 9662 7555
[email protected] www.publish.csiro.au
Front cover Seeds of Podolepsis gracilis, Slender Podolepsis, by Luke Sweedman. Set in 10.5/13.5 Minion Cover and text design by James Kelly Typeset by James Kelly Index by Russell Brooks Printed by Bookbuilders
Foreword At a time when the world’s plant biodiversity and ecosystems are being destroyed at alarming rates, it is most appropriate – and highly desirable – that plant biologists in Australia are devoting time and resources to preserving through seedbanking the species richness of that part of Gondwana. While seedbanking will not conserve ecosystems, it will at least conserve biodiversity, and thus genetic diversity, ex situ. This book is about the biology, collection, storage and use in conservation and restoration of seeds of native Australian species, with emphasis on those that occur in Western Australia. The authors represent a wide range of expertise on the various basic and applied aspects of seed biology it covers. The core of Australian Seeds contains much useful advice about seed collecting tools, equipment and procedures; how to determine the right time to collect seeds; sampling strategies; collecting seeds of rare species; and how to keep good records about seed collections. It also contains much well thought-out, and thus very good, advice on handling of seeds in the field prior to return to the storage facility and on drying and cleaning seeds after returning from the field, including an overview of equipment needed in processing of seeds; seed-cleaning tips for the ‘unusual’ genera Banksia and Dryandra (Proteaceae); and how to assess and prevent or minimise damage to seeds by pests and diseases. There is also a lucid presentation about laboratory storage of seeds and of testing them for purity, moisture content, viability and germination. There are many photographs that complement nicely the subject matter discussed in the text. Guidelines for collecting seeds of species of the common Australian families Amaranthaceae, Asteraceae, Fabaceae, Mimosaceae and Myrtaceae, and of more than 260 selected genera in these and other families are covered in a separate chapter. In chapter 9, the excellent photographs of seeds of more than 1200 native Australian species illustrate the diversity and beauty of Australian seeds. These photographs also can be used as a ‘visual guide’ for identifying the species that produced the seeds. This chapter in itself
is a major photographic contribution to the diversity and beauty of seeds. In contrast to the detailed advice on how to collect, process and store seeds of Australian plants, Australian Seeds contains very little information on how to germinate them. Although studies have been done on dormancy and germination of seeds of many Australian species, no attempt has yet been made to organise the data and fit them into a dormancy classification scheme to infer, either from taxonomic relationships or from results of studies on dormancy and germination of a taxonomic group, what kind of dormancy may be present in seeds of species for which information is not available. Thus, we suggest that the next step in enhancing knowledge about the biology and technology of seeds of Australian plants should be an attempt to classify them with respect to kind of dormancy. This may not be as difficult as it at first might seem to be. For example, seeds of most species of Asteraceae, Myrtaceae and Poaceae are likely to have (non-deep) physiological dormancy (and some perhaps no dormancy at all) and those of Fabaceae and Mimosaceae physical dormancy (i.e. water-impermeable seed or fruit coat). Australian Seeds is an excellent contribution to plant conservation and restoration in Australia, and the editors and all the contributors are to be congratulated for making the information available in a single volume. Although the book is about seeds of Australian species, it will be of considerable interest and use to people involved in seedbanking and/or plant conservation and restoration worldwide. Also, it will be greatly appreciated and enjoyed by people who are fascinated by the beauty and diversity of seeds. Jerry M. Baskin Department of Biology, University of Kentucky, Lexington, USA. Carol C. Baskin Department of Biology and Department of Plant and Soil Science, University of Kentucky, Lexington, USA. v
Commendation Seeds are vital elements for a sustainable global future. Knowing how to identify, collect, store and germinate seeds is essential to make optimum use of this important resource, especially the poorly known seeds of a large range of dryland species. We are delighted to see this book, focused on seeds of the unique Australian flora, published in such an accessible and beautiful format. The book represents the outcome of years of hard work and collaboration by many individuals and organisations. All are to be congratulated for setting such a high international standard – a model for other countries to emulate. Our organisations take special pride in playing significant roles in seeing Australian Seeds through to publication over a 10-year gestation period. We know the book will prove immensely useful, and wish it the long shelf life it so richly deserves. Roger Smith Head of Seed Conservation Department Royal Botanic Gardens, Kew Director, Millennium Seed Bank Project, 1998–2005. Stephen Hopper Professor, Plant Conservation Biology School of Plant Biology, The University of Western Australia CEO Botanic Gardens and Parks Authority, Kings Park and Botanic Garden, 1992–2004.
The development of this book was generously funded by the Millennium Seed Bank Project.
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Contents Foreword
v
Commendation
vii
Acknowledgements
xi
Preface
xiii
Contributors
xv
1
Introduction
1
Clare Tenner, Stephen Hopper, David Merritt, Anne Cochrane and Luke Sweedman
2
Australian seeds through time
5
Stephen Hopper, Kingsley Dixon and Robert Hill
3
Seed and fruit structure
11
Paul Wilson and Margaret Wilson
4
Seed biology and ecology
19
David Merritt and Deanna Rokich
5
Seed collection in the field
25
Luke Sweedman and Grady Brand
6
Drying and cleaning seeds after collection
41
Luke Sweedman
7
Seed storage and testing
53
David Merritt
8
Seedbanks and the conservation of threatened species
61
Anne Cochrane and Leonie Monks
9
Australian seeds: a photographic guide
67
Luke Sweedman
10 Collection guidelines for common Australian families and genera
173
Luke Sweedman and Grady Brand
Appendix 1: Seed germination records
199
Appendix 2: Specimen vouchers for the seed photographs
220
Appendix 3: List of common names
229
Appendix 4: List of botanical names
241
Glossary
253
References
255
Index
256
ix
Acknowledgements Thanks to Chris Damon and Chris Chaperone who worked hard on the photography; Peter Maloney from the Western Australian Department of Agriculture who demonstrated the use of the glass plate system; Mark Saxon for support and edits; Nathan McQuoid, Guy Groenewegen, Stephen Ashworth and Digby Grounds for their friendship and encouragement; Pauline Fairall for her support; and Peter Luscombe for providing access to photographs. Thanks to the original editorial committee: Steve Hopper, Kingsley Dixon, Stephen Forbes and Roger Fryer for their patience and enthusiasm. Special thanks to Grady Brand for sharing his knowledge, vision and passion for the Australian flora. Thanks also to Trevor Hein for his exceptional editing of the photographs, Russell Barrett and Eng Pin Tay for reviewing and updating the botanical names; Mark Webb for his support; Mike Lloyd for providing seeds from the eastern states of Australia; and Tim Pearce from the Millennium Seed Bank Project, who has become an integral part of the Kings Park Seed Centre’s future direction and was able to help with funding the final publication. Thanks to Carol and Jerry Baskin for providing comments on the manuscript, kindly writing the foreword and showing such excitement when viewing the photographs. Special thanks to Stephen Scourfield for sharing many great times together travelling in the bush and for his
unstinting professional help in putting the book back on track when it was threatening to unravel. Thanks also for allowing the use of many of his brilliant photographs in the book. We gratefully acknowledge the contribution of Willie Kullmann for compiling the initial set of seed germination data in Appendix 1, and the nursery staff of Kings Park and Botanic Garden who collected the data over 40 years. The authors of Chapter 4 thank Annemarie Menadue for kindly providing the illustrations; the authors of Chapter 8 thank the staff and volunteers of the Department of Conservation and Land Management, particularly Sarah Barrett and Gina Broun, for assistance with seed collection and translocation planting and monitoring. Luke Sweedman Curator Western Australian Seed Technology Centre Botanic Gardens and Parks Authority Kings Park and Botanic Garden Perth, Western Australia David Merritt Research Scientist Botanic Gardens and Parks Authority and the University of Western Australia Perth, Western Australia
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Preface This book began more than 10 years ago with an idea by Dr Stephen Hopper, then Chief Executive of the Western Australian Botanic Gardens and Parks Authority. He suggested we compile the years of accumulated knowledge and experience of the Botanic Gardens staff working with seeds and publish it in a form suitable for the general reader. Over the years, the work evolved and progressed with the help of many people and the book now contains input from several organisations across Australia and overseas. The completion of this book is due mostly to the staff at the Botanic Gardens and Parks Authority, many of whom helped directly, and all of whom share a great vision and passion for the Australian flora and for Kings Park itself, which is such a special place in Western Australia. Australian Seeds covers important aspects of the biology, collection, storage and use of seeds in conservation and restoration. It encapsulates much of what is currently known about collecting and storing seeds, with information collated over the last 10 years in which time the science of seeds has been moving at a rapid rate. The book can be used to identify seeds of more than 1200 Australian species and many genera, with photographs showing their diversity, beauty and significant variations. The practical and scientific information relates to seeds across Australia – in fact, seeds anywhere. Many of the major genera, such as Eucalyptus, Acacia and Grevillea, are common throughout Australia. However, since half of Australia’s species occur in Western Australia, it is appropriate that many of the species examples in this guidebook are from this part of the continent. The book fully exploits the authors’ deep knowledge and experience of this vast region, stretching some 3000 km south to north, from a granite coast buffeted by the raw weather patterns of the Southern Ocean, to the tropical, tidal mangroves of the Kimberley, and the deserts between. Chapter 2 explores the evolution of seeds of Australian plants through time, tracing the fossil and geomorphologic records of the Australian continent
since the Devonian, when land plants evolved. An appreciation of the role that seeds play in ensuring the continuation of a species in the face of changing environments (periods of glaciation, global warming, global aridity) provides an insight into the reason behind the remarkable diversity of seed sizes, shapes and germinationtiming cues we see today. The reader is introduced to the morphology of Australian seeds and their fruits in Chapter 3. It shows the array of shapes and sizes of seeds and fruits and explains and illustrates many of the botanical terms relating to the description of seed and fruit morphology. Chapter 4 discusses aspects of seed ecology, describing some of the adaptations Australian species have developed in order to time seed release and germination to the time of year which will maximise seedling establishment in habitats which are often subjected to a high degree of environmental stress, including periodic drought, temperature extremes and fire. Chapters 5 to 7 form the core of the practical guide. Chapter 5 covers in detail the planning required prior to a field trip, the equipment and tools necessary, the sampling strategies for collecting seeds and the documentation essential for a successful collecting trip. This is followed by Chapter 6 which covers the actions required after seed collection, both in the field and upon return to the seedbank. It discusses in detail techniques of seed handling, cleaning and processing, as well as the procedures for drying large quantities of seeds. It also reviews the tools and equipment available for seed processing. Chapter 7 provides an introduction to the steps undertaken in the laboratory to correctly dry, store and test seeds. It outlines drying and storage techniques that will maximise seed longevity and describes current international, best-practice standards. It also outlines the methods employed for seed moisture, viability and germination testing, and includes tips for assessing data and determining the success of a particular storage regime.
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Australian Seeds
The role that seedbanks play in conservation, restoration, horticulture and education, is illustrated in Chapter 8, which highlights the range of uses of native seeds. Several case studies illustrate how seedbanks can contribute to the protection and recovery of species that are perilously close to extinction, unfortunately an increasingly common scenario in the modern world. The beauty of Australian seeds is showcased in Chapter 9, which contains photographs of 1260 Australian seeds. This chapter can be used as a visual guide for identifying species and to appreciate the incredible diversity of Australian flora, reflected in the diversity of the seeds. Chapter 10 describes specific collecting techniques for some of the main plant families, giving details for more than 260 genera of Australian plants. The genus Corymbia is recognised in this book as a separate genus to Eucalyptus. The book largely follows the family classification of the Angiosperm Phylogeny
xiv
Group.* Notable changes in this system compared to recent books such as the Flora of Australia series include a significant reclassification of the lilioid monocotyledons (Liliaceae and Anthericaceae), and a broad definition of the legume family (Fabaceae). The cotton family (Malvaceae) and relatives Sterculiaceae are included in the broad concept of Malvaceae. At the end of the book is a list of germination times for Western Australian species. These provide useful information for seed propagation planning. This is followed by a reference guide to the seed photographs, linking them to the herbarium records at the Botanic Gardens Park Authority Herbarium, Perth, Western Australia. There is also a full glossary of terms. All photographs are by chapter authors unless otherwise noted. * Angiosperm Phylogeny Group (2003). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141, 399–436.
Contributors EDITORS Luke Sweedman
Luke joined the Botanic Gardens and Parks Authority in 1990, initially working as the seed collector. He now holds the position of Curator for the Western Australian Seed Technology Centre at Kings Park. His role has continued to evolve with an increasing focus on the storage of species for both local and international threatened flora programs as well as providing material for display for the Botanic Gardens at Kings Park. Dr David Merritt
David is a Research Scientist at the Botanic Gardens and Parks Authority and The University of Western Australia. He has worked with native seeds since 1997 and his research interests include seed storage and dormancy, and the use of seeds in restoration.
OTHER CONTRIBUTORS Grady Brand
Grady is the Curator of the Western Australian Botanic Gardens. Over the last 27 years, while employed by the Botanic Gardens and Parks Authority, Grady has played an active role in assisting and overseeing the collection, propagation, cultivation and display of the Western Australian flora, including four floral displays held at International Horticultural Exhibitions (UK and Japan). Anne Cochrane
Since 1993 Anne has been the Manager of the Department of Conservation and Land Management’s Threatened Flora Seed Centre, a seed conservation facility for rare, threatened and poorly known Western Australian taxa. She is a Senior Research Scientist with many years of seed-based field and laboratory experience. Professor Kingsley Dixon
Kingsley is the Director of Science at the Botanic Gardens and Parks Authority. He has more than 20 years’ experience in researching the ecology and physiology of Australian native plants and ecosystems and leads a multi-disciplinary science group comprising botanical and restoration sciences. Roger Fryer
Roger is currently Manager, Horticulture and Assets at Kings Park and Botanic Garden and was previously Curator, Living Collections, and Nursery Manager. In these positions Roger has been involved in propagation and seed germination records and in overseeing the work of the Western Australian Seed Technology Centre.
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Australian Seeds
Professor Robert Hill
Robert is Head of the School of Earth and Environmental Sciences at the University of Adelaide and Head of Science at the South Australian Museum. For the past 25 years he has been researching the fossil evidence for the evolution of the modern southern Australian vegetation based on the plant macrofossil record. He has concentrated on the major families Nothofagaceae, Proteaceae and Podocarpaceae, including research on fossilised reproductive structures. Professor Stephen Hopper
Stephen was Director and CEO of Kings Park and Botanic Garden from 1992 to 2004, and is now Foundation Professor of Plant Conservation Biology at The University of Western Australia. He has expertise in plant evolutionary biology, systematics, biodiversity conservation and granite outcrop floras. Leonie Monks
As a Research Scientist with the Department of Conservation and Land Management, Leonie has been developing effective translocation techniques for threatened Western Australian plant species since 1998. The promotion of successful seed germination is an integral part of this research. Dr Deanna Rokich
Deanna is the Senior Restoration Ecologist at the Botanic Gardens and Parks Authority. Her research career has focused on regenerative techniques and seed ecology of biodiverse ecosystems throughout Western Australia, particularly for restoration of mined sites and urban bushland. Clare Tenner
Clare is the International Programme Officer for the Millennium Seed Bank Project. She oversees and coordinates the activities of the MSBP International Programme, including monitoring and reporting on progress towards the Project goals and developing links to other appropriate biodiversity initiatives. Margaret Wilson
For three decades Margaret has produced thousands of illustrated botanical descriptions for research publications in which Australian native fruits and seeds feature as key elements for plant identification. A dedicated conservationist, Margaret propagates native seeds for use in nature reserves and believes a greater cultural appreciation of the vital role of seeds in conservation is essential. Paul Wilson
For more than 50 years Paul has been involved with plant taxonomy. Initially at the Kew Herbarium, England, he worked on the plants of Mexico. After moving to Australia in 1958 he focused his research on the families Asteraceae, Chenopodiaceae and Rutaceae, seeds and fruits being particularly significant in their classification.
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CHAPTER 1
Introduction Clare Tenner, Stephen Hopper, David Merritt, Anne Cochrane and Luke Sweedman
Some 25 000 species of vascular plants – 10% of the world’s total – are found in Australia. At least 85% of these species are endemic, an outcome of 42 million years of isolation. Two-thirds of the Australian continent is arid, with less than 300 mm of rain a year. This area stretches from the Pilbara region of the north-west to the southern Nullarbor, where the desert meets the coast. Surrounding the arid zone on three sides are broad semiarid belts in which woodlands, mallee, and sclerophyll shrublands are prevalent. Salt lakes with uncoordinated drainage are common in broad valley floors, particularly in the west and south of the semi-arid zone, but the east is occupied by the bulk of Australia’s largest river system, the Murray-Darling. The wetter parts of Australia occupy less than a fifth of the continent, south and eastwards of the eastern highlands, across the tropical north and in a small isolated region of the south-west. Vegetation is complex, matching the topography and geology of these areas. The wettest places, often with deep fertile soils in eastern and northern Australia, are occupied by rainforests, while shallow soils in the highest rainfall areas have stunted woodlands and heaths. Wet sclerophyll forests occupy fire-prone sites and contain immense hardwoods such as mountain ash (Eucalyptus regnans) in the southeast and karri (Eucalyptus diversicolor) in the south-west. The highest mountains support alpine vegetation and stunted sclerophyll communities. Less fertile
soils on rock outcrops throughout the wetter parts of Australia also have sclerophyll shrublands and stunted woodlands. Freshwater lakes and streams are strongly seasonal, as are coastal estuaries and bays into which the latter discharge. Coastal floras include mangroves and the usual cosmopolitan plants of dunes and strand, while adjacent Australian marine environments are noteworthy in the north for their coral communities of the Great Barrier Reef on the east coast and such places as Ningaloo Reef on the west coast. Across Australia, there are three key floristic elements: woody evergreens, rainforests and the cosmopolitan plants. The bulk of the 25 000 species are endemic evergreen sclerophyllous plants of forests, woodlands, mallee, shrublands, sedgelands and grasslands. Particularly noteworthy is the dominance of three woody, evergreen genera: Eucalyptus/Corymbia (more than 900 species) and Acacia (more than 1100 species). Spinifex hummock grasses of the genus Triodia are prominent over vast desert areas. Species-rich families in Australia include the Proteaceae (banksias, grevilleas, etc.), Myrtaceae (eucalypts, melaleucas, etc.), Ericaceae (Epacridaceae – southern heaths), and Restionaceae (southern rushes). Occupying about 5% of the continent, the south-west of Western Australia is especially rich in the Gondwanan element of the Australian flora, with an estimated 8000 species, 50% of which are endemic to the region. 1
Australian Seeds
The cosmopolitan element of up to 3000 species occupies coastal habitats, saltlands, wetlands and alpine or mountainous areas. Typically, endemism is lower in this component of the flora. The Australian flora is, indeed, extraordinary. And never has an appreciation of its seeds, and the need to conserve them, been greater. SEEDBANKING IN CONSERVATION: THE INTERNATIONAL CONTEXT
Tasmanian rainforest, a living Gondwanan museum.
In contrast, the extensive central Australian desert region, occupying one-third of the continent, has only 2000 species. The ancient rainforest element covered only 1% of the Australian landmass at European colonisation. Rainforests occur in scattered sites from Tasmania to north Queensland and westwards across the tropical Northern Territory to the Kimberley region of Western Australia, and contain upwards of 2000 species, many endemic to Australia. The rainforests are living Gondwanan museums – fragmented and depleted relicts of vegetation that covered parts of the continent before the onset of Tertiary aridity after Australia drifted north from Antarctica, beginning 42 million years ago. These rainforest patches differ significantly in composition, with three major floristic groups recognised. There are cool-wet temperate rainforests of Tasmania, Victoria and New South Wales, hot-wet subtropical-tropical rainforests from near Sydney north to Queensland and the wettest parts of the Northern Territory, and hot-dry semi-deciduous or deciduous rainforests and vine thickets extending from the Kimberley across to north Queensland and south into semi-arid New South Wales. 2
An understanding of the role of seeds in conservation of the world’s biological diversity is necessary to appreciate the resources now dedicated to working with seeds. It is well recognised by the global community that biodiversity is being destroyed irreversibly by human activities and that a major effort is needed to better understand and conserve biodiversity. In January 2005, the Paris Declaration on Biodiversity noted that humans were altering the environment at unprecedented speed, with species being lost at a rate about 100 times faster than the average natural rate. The large-scale loss is irreversible, but the declaration calls for a major effort to discover, understand, conserve and use biodiversity sustainably. In 2002 the Parties to the Convention on Biological Diversity (CBD) adopted a strategic plan with a mission to achieve by 2010 a significant reduction of the current rate of biodiversity loss. This was later endorsed by the World Summit on Sustainable Development. The CBD recognises that ex situ (off-site) measures – collecting seeds and then keeping them in seedbanks, for example – have an important role to play in the conservation of biodiversity. The CBD definition of biodiversity recognises diversity within species, between species and at the ecosystem level. Many studies have shown the threats that face biodiversity occur at all three levels. For example, at the ecosystem level, models suggest that by the year 2032 up to 48% of ecosystems could be converted to agricultural land, plantations or urban areas, compared to 22% today. At the species level it is thought that as many as two-thirds of the world’s plant species are in danger of extinction in nature during the course of the twenty-first century. With regards to genetic diversity, it is estimated that 16 million populations are lost annually. In Australia alone, 2891 individual ecosystems have been identified as at risk, and 1595 native animal and plant species. The biggest direct cause of species loss is habitat loss and degradation – this affects 91% of all threatened plant species described in the 2000 IUCN red list. Habitat can
Chapter 1 – Introduction
be lost through conversion for, or intensification of, agriculture, urbanisation and infrastructure development, amongst other things. Protected areas can help safeguard habitat, but there are limits to the area of land that can be covered. It takes time to establish protected areas and it can be difficult to situate them for the optimal protection of plant species. Even in well-protected areas plants are subject to further threats including climate change, invasive alien species, over-exploitation by humans and manmade and natural disasters. The Intergovernmental Panel on Climate Change predicts that the synergy between the stresses of climate change, habitat loss and fragmentation, and alien species will lead to extinctions. In Australia additional threats to biodiversity include dieback/disease, salinity, overgrazing, feral pests, and inappropriate fire regimes. The root causes of biodiversity loss are, of course, more complicated to unravel, but include elements such as demographic changes, poverty and inequality, macroeconomic policies and trade practices and patterns of consumption. These will take time and political will to tackle. In the meantime seedbanks can play a significant role by conserving inter-species and intra-species diversity. The collection and storage of seeds is not new. Many peoples have done this for millennia. Certainly, since the beginning of agriculture, most of the world’s food supply has relied on seeds that can be harvested and stored for a period of time. However, the establishment of native seedbanks for biodiversity conservation is a relatively recent occurrence, as is the use of stored seed in flora recovery projects. In some cases, ex situ conservation represents the only option available if the remaining natural populations are to be conserved in the face of destruction of their habitat. Actions to conserve individual species contribute in a fundamental way to broader conservation objectives, even if the species themselves are not highly threatened. Seedbanking cannot directly protect biological diversity of ecosystems, but it can ensure the protection of genetic diversity. Material can be provided for species and ecosystem recovery, and it has proved a cost-effective source of material for research. Investigations into seed germination and storage behaviour maximise the value of the material, and seedbanks have made an important contribution to education and public awareness. Ex situ conservation is a critical component of an integrated global conservation programme, and seedbanking is one of the most valid and widespread
methods used at present owing to its simplicity and economy in terms of technology, infrastructure, manpower and operating costs. It is possible to maintain large samples with wide genetic representation at an economically viable cost. Of the 9000 plant species whose storage characteristics are known, 92% have desiccation-tolerant seeds and are expected to remain viable in storage for at least 200 years. Today there are around 150 seedbanks found within the world’s botanic gardens. In addition, many national crop and tree seedbanks are increasingly moving into conservation of wild plant species. In any case, seed collections are a readily accessible and cost-effective source of material for research. Material is quickly and easily accessible to researchers, without the need to carry out expeditions or to over-exploit wild populations. Terms and conditions can be attached to the supply of this material which ensure the fair and equitable sharing of any subsequent benefits. The CBD provides the international framework for activities on biodiversity. The overall objectives of the CBD are conservation of biological diversity, sustainable use of components of biological diversity, and fair and equitable sharing of the benefits arising from the use of genetic resources. As has been discussed above, seedbanks have a role to play in meeting all three of these objectives. The CBD emphasises that the fundamental requirement for the conservation of biodiversity is in situ (on-site) conservation, but that ex situ measures have an important role to play.
The Millennium Seed Bank, Wakehurst Place, UK, is an example of a modern, well-equipped seedbank.
3
Australian Seeds
The Biodiversity Conservation Centre, Kings Park and Botanic Garden, Perth, Western Australia.
The CBD has been ratified by the governments of 187 countries, including Australia. It provides international political endorsement of the work of ex situ programmes, such as the Millennium Seed Bank Project, an international collaborative plant conservation initiative based in the United Kingdom. This worldwide effort aims to safeguard 24 000 plant species globally against extinction and has already successfully collected and stored seeds of virtually all the United Kingdom’s native flowering plants. This project is evidence of the resources now being directed into seedbanking for conservation. Even if species are lost in the wild, the work of seed collectors will ensure that plants will be available for use in future conservation and restoration efforts. Botanists have been at the forefront of conservation developments, and led by example with the development of the Global Strategy for Plant Conservation (GSPC). The Strategy originates from a resolution at the 16th International Botanical Congress, held in St. Louis, USA, in 1999. It was developed by a globally representative group of botanical institutes, non-governmental organisations and inter-governmental organisations, and was adopted by the Parties of the CBD in 2002. The Global Strategy for Plant Conservation provides a framework for actions at global, national and local levels to under-
4
stand and document plant diversity, conserve plant diversity, use plant diversity sustainably, promote education and awareness about plant diversity and build capacity for the conservation of plant diversity. The Global Strategy for Plant Conservation includes 16 targets to be reached by 2010. One calls for ‘60% of threatened plant species in accessible ex situ collections, preferably in the country of origin, and 10% of them included in recovery and restoration programmes.’ At a global level the lead organisations for this target are Botanic Gardens Conservation International (BGCI) and the International Plant Genetic Resources Institute (IPGRI). Meeting this target is no simple task. At present we do not even know how many species there are, let alone which are threatened. The GSPC currently states that 10 000 threatened plant species are maintained in living collections (botanic gardens, seedbanks and tissue culture collections), representing 30% of known threatened species. This leaves another 10 000 to be collected and conserved by 2010. However, more recent figures suggest that the number of threatened species may be around three times those used in the GSPC. The most important thing for seedbanks is to make information available on the species they hold, and to work together to avoid a duplication of effort. Some coordinated networks are already established. For example, the Millennium Seed Bank Project is working with partners from 17 countries worldwide to collect and conserve 24 200 species by 2010. Regional networks include the European Native Seed Conservation Network and the African Botanic Garden Network. There are also challenges regarding the quality of the collections. This will affect the usefulness of the collections for recovery and restoration programmes. There is little information at the moment on whether existing collections are genetically representative and attention also needs to be paid to the quality of storage. Finally, there is a challenge in ensuring that collections are held in their country of origin. This requires long-term commitment from the home governments but will also require technical support and assistance from established seedbanks. Australian seedbanks have a clear role to play here.
CHAPTER 2
Australian seeds through time Stephen Hopper, Kingsley Dixon and Robert Hill
The evolution of seeds was a major step in enabling plants to colonise land beyond wetland habitats or their margins. Seeds provided an escape from the requirement for free water to ensure sexual reproduction. This requirement still applies to present-day mosses, liverworts, ferns and fern-allies, and explains why these plants are confined to habitats where water is prevalent when they reproduce. The other advantages of seeds are the protection from desiccation, predators and pathogens they afford to the embryo, and the nutrients they provide for germination and early growth. With this revolutionary reproductive strategy, seed plants have been able to occupy most terrestrial landscapes. The essential precursor to seeds was the transition from plants producing spores of the same size (homospory) to producing two sizes: megaspores and microspores (heterospory). This occurred around 400 million years ago in groups such as the horsetails, tassel ferns, spike mosses, quillworts, ferns and other groups now extinct. Megaspores were precursors to ovules and microspores were precursors to pollen. By 370–354 mya (million years ago), fossil megaspores had developed an outer protective coating, and had become the first ovules or unfertilised seeds. At the same time, pollen was evolving from microspores. The microspores release flagellated structures that swim through water to fertilise immobile female gametes,
whereas pollen produces a tube through which male gametes are transferred directly into the ovule. The ovules also evolved pollen reception mechanisms, such as hairs, funnels and lobes to trap wind-dispersed pollen, and sticky pollination droplets borne on tentaclelike projections. The latter characterise cycads, conifers and their relatives to this day, whereas flowering plants have an enclosed protective coating with a single pore (the micropyle) to provide access for the pollen tube. This has the advantage of extra protection from desiccation, predators and pathogens, and enables evolution of elaborate seedcoats to facilitate dispersal away from the mother plant. At the same time as these revolutionary reproductive innovations were evolving, terrestrial plants had also increased their size and stature, attaining heights to 35 m. This was a time of remarkably high atmospheric CO2 concentrations and therefore high global temperatures. As plants evolved ovules and seeds, and increased their biomass as trees, they were able to survive and reproduce over many landscapes, mesic and arid, extensively colonising the land. This global greening of the land caused atmospheric CO2 to plummet, resulting in global climatic cooling in the ensuing period. Thus, the massive glaciation of the Australian part of the global supercontinent Pangea from 320 to 270 mya may be directly attributable to the effects of the evolution 5
Australian Seeds
of the seed. For this reason, our flat, deeply weathered continent, the product of unimaginable ancient glacial forces, owes its essential character to the humble seed. The earliest seed plants were pteridosperms (seed ferns) and cordaites. Seed ferns had fern-like foliage (but were not closely related to ferns) produced on plants ranging from vines to trees. They survived for more than 200 million years, overlapping in time with the earliest flowering plants. Cordaites were trees with strap-like leaves similar to today’s araucarian conifers. Although prominent in Australian periglacial forests together with seed ferns and giant horsetails, cordaites were extinct by 240 mya. Other groups of seed plants, including gymnosperms such as the cycads, ginkgoes and conifers, first appeared as fossils about 280 mya, but did not achieve dominance of global vegetation for 80 million years until the world became a hothouse at 200 mya (Figure 2.1). This global warming that melted the glaciers is attributed to widespread aridity and increased continentality owing to the formation of Pangea, which was centred on equatorial latitudes. Massive mountain ranges that were pushed up owing to the collision of Gondwana with its northern hemisphere counterpart Laurasia are also likely to have increased continentality, blocking moisture-laden oceanic winds from penetrating inland, and increasing aridity, even at the equator. The earth was inherited by plants capable of surviving and reproducing in arid environments. The age of seed plants had arrived. Interestingly, today seed dormancy predominates in
arid to semi-arid and temperate environments but is not so prevalent in tropical rainforest.2,3 The move into arid environments thus undoubtedly was facilitated by the evolution of dormancy mechanisms among early seed plants. Physiological dormancy, where the embryo has low growth potential and cannot overcome the mechanical constraint of the seed or fruit coat, occurs widely among extant seed plants.4,5 Less common but equally widespread phylogenetically (except for rosids) are morphological dormancy and morphophysiological dormancy. Physical dormancy, involving the presence of water-impermeable palisade-like layers of cells in seed or fruit, has evolved only in select angiosperms, especially Malvales. SEED PLANTS RULE
By the Jurassic (208–144 mya), the Australian flora was dominated by seed plants such as araucarian and podocarp conifers, bennettitaleans, and cycads, as well as ferns (Figure 2.1). Dinosaurs diversified, as did the first birds, with likely significant impacts on the disturbance regime experienced by plants. Such disturbance continued into the Cretaceous (144–65 mya), which was a period of climatic change in Gondwana to warm conditions. Conifer-dominated vegetation was progressively replaced by rapidly radiating angiosperms, especially in the latter half of this period. An excellent example of an angiosperm genus with seeds adapted for a disturbance-based ecology is Nothofagus.6 This genus has one of the longest fossil
Fig. 2.1. The number of species recorded through time of major land plant groups from 450 mya to the present. 1 6
Chapter 2 – Australian seeds through time
A
B
D
E
C F
G
5 mm
Fig. 2.2. Cupules of fossil and extant species of Nothofagus. In the subgenus Brassospora (A, B, C), the cupules have two woody valves that enclose one or three fruits. In the subgenera Lophozonia (D, E) and Nothofagus (F, G), the cupules usually have four cupule valves enclosing three fruits. A = N. peduncularis (Early Oligocene c. 30 mya, Little Rapid River, Tasmania), B = N. cooksoniae (Early Oligocene c. 30 mya, Little Rapid River, Tasmania), C = N. smithtonensis (Early Oligocene c. 30 mya, Little Rapid River, Tasmania), D = N. glandularis (Late Oligocene–Early Miocene c. 24 mya, Balfour, Tasmania), E = N. glandularis (Early Oligocene c. 30 mya, Little Rapid River, Tasmania), F, G = N. bulbosa (Early Oligocene c. 30 mya, Little Rapid River, Tasmania).
records among flowering plants, reaching back approximately 80 million years to its first appearance somewhere around the Antarctic Peninsula and southern South America (at a time when this was continuous land). The early fossil record of Nothofagus is provided by the very distinctive pollen and later by leaves. However, in southeast Australia there is a very good record of fossil cupules that bear the very simple fruits (Figure 2.2). The fossil record of Nothofagus in Australia demonstrates that the genus was very diverse here especially around 25–40 mya. This included all four of the extant subgenera (Figure 2.2), and probably some extinct subgenera as well. Today Australia has just three Nothofagus species, in two subgenera. This decline in
diversity underestimates the true decline in the genus over this time period, since at its height Nothofagus must have dominated large tracts of vegetation, with its pollen dominating both spatially and temporally over much of Australia for tens of millions of years. The disturbance-based regeneration ecology of fossil Australian Nothofagus is supported by two lines of evidence. First, large-scale land disturbances may have been much more common in Australia when Nothofagus was dominant in the vegetation. Apart from the impact of large dinosaurs, geological processes were also active. This was the time when Australia was separating from Antarctica and the extensive rift valley across southern Australia would have been a highly disturbed region. 7
Australian Seeds
A
B
C
E
F
G
1 mm D
Fig. 2.3. Fossil seeds from the Early Oligocene (c. 30 mya) Little Rapid River sediments in north-west Tasmania. None of these have been identified with certainty, and they are representatives of a very diverse seed flora at this locality. All scale bars = 1 mm. A = LRR1-302, B,C = LRR1-2216, D = LRR1-306, E = LRR1-356, F = LRR1-308.
Furthermore, Australia had a much more active volcanic history during much of the past 65 million years compared with today and some of these volcanoes were very large. Second, the cupule and fruit morphology of many of the fossil Nothofagus in southern Australia were almost identical with those produced by species that live today in very disturbance-prone areas. It is likely, therefore, that Nothofagus evolved in an area with a high rate of natural disturbance and throughout its history this has continued to be an important factor in its distribution. The relatively recent shift away from high natural disturbances in Australian wet forests (excluding fire) has led to a decline in Nothofagus diversity and dominance. There are many Australian fossil seeds whose relationships with living species are not as clear as for the Nothofagus fossils (Figure 2.3). This signals great oppor8
tunities for further research on the evolution of Australian seeds. It is clear that seeds have provided a mechanism of fundamental importance to plants during major periods of global aridity. The earliest seed plants colonised arid lands about 400 mya and their sheer abundance reduced atmospheric CO2 levels so much as to precipitate global cooling and the greatest and longest glaciation seen on earth (320–270 mya). Then conifers, cycads and ginkgoes came to dominate the subsequent hothouse world. Angiosperms likewise rose to ascendancy over conifers during the warming Cretaceous. Most recently in Australia, the onset of aridity around 30 mya and its intensification since 15 mya has similarly seen the proliferation of arid-adapted angiosperms at the expense of rainforest taxa.
Chapter 2 – Australian seeds through time
SELECTION PRESSURES ON AUSTRALIAN SEEDS
Seeds are produced as part of the reproductive system of plants. A familiar experience of many Australian seed collectors is the relatively low numbers of seeds produced by some genera such as Banksia, Macropidia, Verticordia and Lechenaultia. Often this is owing to complex genetic systems associated with inbreeding in small populations,7 especially on the ancient landscapes of south-west Australia.8 Careful experimentation and observation is needed to resolve the precise causes. The tremendous variation in seed size, shape and structure is the product of evolution through a complex and varied environmental history. Seed attributes represent a compromise between selection pressures for seed development, for seed dispersal and for germination and establishment of seedlings.9 Seed development may be so reduced as to be rudimentary, as in orchids, or elaborately complex, to ensure against desiccation, predation or disease infection. Dispersal by wind, water or animals selects for diverse seed architecture and biochemistry. Germination requirements do likewise, be they heat, smoke, scarification, cold treatment, aging or other factors. Seedling establishment brings to bear selection for sufficient resources and hormonal systems to ensure growth.
ular soil bacteria thought to produce growth factors for promotion of germination. The biological costs for this level of specialisation is indeed high. Orchids produce the smallest seed in the flowering plants (some less than a microgram in weight) to enable production of seeds per pollination event in the thousands and even millions. These seeds fall into crevices and spaces in the soil profile and await infection by a beneficial fungus. With such a small size and little or no embryonic differentiation, seed of Australian terrestrial orchids are particularly shortlived in nature – lasting just months or weeks following soil wetting with the opening rains. Without a fungal partner these terrestrial orchid seeds rapidly decay and lose viability. The degree of habitat specialisation between seed and biological agents has been taken to the extreme in the Western Australian underground orchid (Rhizanthella gardneri), where not only is a fungus of a precise type required but that germination will only occur if the fungus is in association with the root system of a specific shrub, the broom honey myrtle (Melaleuca uncinata).10 With this level of ‘habitat matching’ by the orchid, it is no wonder that the underground orchid is also one of Australia’s most endangered orchids! SEED SIZE AND ITS EVOLUTIONARY IMPLICATIONS
ARRIVING ON CUE!
The seeds of early Australian land plants enabled them to disperse an embryo and attendant food stores into habitats depleted of nutrients and experiencing sometimes extremes of seasonality in temperature and moisture availability. Overcoming nutrient deficiency in the soils was accommodated by ensuring the seed possessed sufficient on-board nutrient resources to sustain the seedling until the young plant could resort to de novo uptake and synthesis. In some cases this has been taken to the extreme with Australian Proteaceae capable of surviving on maternally derived nutrients for the first year and half of seedling growth. But coping with aridity and high temperatures presented particular problems for the seed – ingeniously solved by the adoption of a complex array of dormancy release cues in Australian species including temperature and external agents such as heat, nitrate and smoke. The seeds of terrestrial orchids are unique among plants in linking dormancy release to the intervention of a biological agent – in their case a specific mycorrhizal fungus and for some species in a partnership with partic-
Seed mass is one of the most important aspects of ecological variation among coexisting species. Sizes range from the dust-like seeds of orchids weighing a millionth of a gram to the double coconut whose seeds can attain 20 kg. There are fundamental trade-offs between producing many small seeds each with a low probability of establishment or fewer larger seeds better provisioned and able to withstand greater environmental stress once germinated.11 Seed mass tends to increase in shaded environments such as forests, whereas no clear trend applies to nutrient-poor versus nutrient-rich environments. Aridity and seed mass similarly exhibit little correlation. Indeed, apart from differences owing to shade, the major arena of variation in seed mass is usually within habitats. Predation is another consideration pertinent to seed size variation. Intuitively, large seeds would be expected to endure higher predation risks, but data acquired for 170 Australian species from arid, subalpine and temperate east-coast environments has indicated no significant relationship between seed mass and survivorship after exposure for 24 hours to seed predators. Causes of variation in seed size must lie elsewhere, unless the 9
Australian Seeds
Southern Beech (Nothofagus cunninghamii), Tasmania.
extinction of consumers of large seeds such as giant Australian mihirungs (goose-like birds) explains this surprising result. Other explanations might relate to available sunlight. Under low light conditions, for example, small-seeded species etiolate rapidly at the expense of root mass, exposing the plant to mechanical breakage and fungal attack to maximise the search for light, whereas largeseeded species do not grow as fast, and invest more in root systems. Should low light persist, large-seeded species have a clear advantage at this early stage of the life cycle. Unravelling the selective regimes and evolutionary
10
complexity of such patterns remains a challenging task for seed biologists. Australian seeds have an exciting and as yet poorly explored evolutionary history. Seeds represent a revolutionary innovation for global plant life in enhancing abilities to survive and reproduce in arid environments. Australia, as the most arid vegetated continent, presents significant opportunities to discover new and surprising things about seeds. In particular, most of the western two-thirds of the continent has experienced 270 million years of uninterrupted terrestrial life on predominantly old, flat, weathered, nutrient-deficient landscapes. This has provided conditions for the evolution of seed attributes that are globally unusual, especially in the south-west where a pocket of oceanically buffered mesic climate has persisted despite the onset of aridity 30 mya. Such unusual evolutionary conditions have been matched perhaps only by those seen in South Africa. As a result, deep dormancy syndromes in Western Australian species are among the most complex known with more major families with intractable dormancy than other similar areas of species richness. Mechanisms for dormancy release are equally complex and involve single and combinational dormancy cues that are environmental, climatic and/or biological with discoveries of new combinations being a regular occurrence. Such discoveries are not only of intrinsic interest. They will be of enormous applied value as well in horticulture, landcare and restoration of disturbed sites. The discovery of smoke as a stimulant for germination of large numbers of previously intractable Australian species is a telling example.12 Its application to Australian plants is barely a decade old, yet smoke has rapidly become an essential part of routine operations in Australian nurseries, landcare and mine-site restoration. The range of Australian seeds illustrated in this book undoubtedly have other stories to tell.
CHAPTER 3
Seed and fruit structure Paul Wilson and Margaret Wilson
GIVEN that virtually all animal (and human) life on Earth is dependent on the plant world, the seeds that give rise to the greater terrestrial portion of this green kingdom deserve our respect. Yet the attention given to seeds is often superficial. A knowledge of the structure of seeds and fruits is of great importance to botany, seedbanks, and for those needing to establish the identity of particular fruits and seeds either during the prosaic, routine examination of seedlots, or for the more specialised study of their presence in soil, in archaeological sites, as contaminants, or even as the subject of forensic or quarantine enquiries. An understanding of seeds and fruits is also required for the study of the medicinal and nutritional values of native plants and their traditional uses. The visual and cultural appreciation of seed and fruit structure and function is similarly important. Fruits with their appealing shapes are a timeless source of inspiration and enchantment. Australia possesses some fascinating forms, and their place in the world of art, flower arrangement and floriculture has still to be fully explored. Both in art and science, the rich variety of colour, scent and taste sensations of fruits and seeds, so important for their dispersal, have a significant role. From the scientific or biomechanical points of view, Australian seeds and fruits are masterpieces of design, superbly adapted to often extreme climatic conditions, impoverished soils, methods of dispersal, and critical
levels of competition and predation; their morphology reflects these factors. It should be borne in mind that the simple classification that follows, detailing the principal types of seeds and fruits found in Australia, has little bearing on the genetic relationships of the different species. Similar looking seeds or fruits can be found in plant families that are not closely related, while vastly different looking ones can occur in the same family. SEED FORMATION
A seed is generally formed from a fertilised ovule. How does this transformation occur? A typical flower is made up of sepals, petals, stamens (the male component), and an ovary (the female component), (Figure 3.1). The ovary consists of a chamber containing one or more compartments and usually bears at its apex a stigma, which is often supported on a style, an extension of the ovary. The ovary is considered to have arisen from a megasporophyll, a leaf that acquired a female function and bore ovules at its margin. The leaf folded around these ovules to form a closed seed-chamber. An indication of this ancient origin may still be seen in the ovaries of some modern-day plants. Each of the one or more ovules contained in the ovary is attached by a stalk or funicle (Latin for ‘string’) to a portion of the ovary called the placenta. 11
Australian Seeds
The ovule (Figure 3.2) at first appears as a domeshaped structure called the nucellus (originally named the ‘nucleus’). From this arises one or more layers of cells, the integuments (Latin for ‘coverings’) which enclose the nucellus, except at the tip where there is a tiny opening, the micropyle (Greek pyla: ‘a gate’). Within the nucellus, through a process of nuclear division or meiosis, several nuclei are formed that have only half the number (the haploid number) of chromosomes found in the flowering plant (which has the diploid number). One of these nuclei becomes the megagamete or egg. Pollination occurs when a pollen grain lands on the stigma of the flower. The grain develops a pollen tube which grows down the style into the ovary. The nuclei in the pollen are also haploid and make up the male gametes which pass through the micropyle of the ovule into the nucellus. One of these gamete fuses with the egg nucleus to become a zygote having the diploid number of chromosomes. The other male gamete fuses with two of the other haploid nuclei in the nucellus to produce an endosperm nucleus which is triploid, because it contains three times the haploid number of chromosomes. This process constitutes double fertilisation. SEED STRUCTURE
At maturity, a seed consists of an embryo, storage tissue and a protective seedcoat. The embryo develops from the fertilised egg-nucleus in the ovule. In dicotyledonous plants it is typically made up of a pair of cotyledons (the seed leaves), an epicotyl (i.e. ‘above the cotyledons’, the embryonic shoot apex), and a hypocotyl (i.e. ‘below the cotyledons’, the embryonic stem and root).
While the fertilised egg-nucleus or zygote develops into the embryo, the endosperm nucleus usually divides repeatedly to form a rich store of food that surrounds the developing embryo, providing it with nourishment (Figure 3.3). This endosperm may be entirely absorbed by the developing embryo, as happens in legumes and crucifers, or it may persist as a food supply for the young plant, as occurs in Boronia and many other members of the Rutaceae family. In many plants such storage tissue in the form of either endosperm or embryo is attractive as a food source to insects, birds, or mammals, as well as to humans. With the growth of the embryo and storage tissue, there is an increase in the size of the ovule and a change in its associated tissues, such as in the funicle and the integuments, as it progressively develops into a seed. The one or two integuments are of particular significance since from them the seedcoat or testa is formed (Figure 3.3), which is usually hard and provides mechanical protection for the seed. The seedcoat in some plants may also secrete chemical inhibitors to ward off competitors. In some instances the seedcoat exudes mucilage when wetted which allows it to adhere to the soil surface. When mature, the funicle usually breaks away from the seed at a point called the hilum, Latin for ‘a very little thing’ (Figure 3.3). The hilum forms a distinctive scar on the seed and becomes covered by a corky tissue. This hilum may be insignificant, as in orchid seeds, or it may occupy a considerable part of the seed surface, as in some legumes. A portion of the funicle that becomes fused to the seed is called the raphe (Greek for ‘a seam’).
stigma micropyle nucellus
integuments egg
petal style
funicle
stamen sepal ovary placenta
Fig. 3.1. Stylised section through flower 12
Fig. 3.2. The ovule
Chapter 3 – Seed and fruit structure
micropyle
testa embryo hilum
hilum raphe
endosperm raphe
endosperm
raphe
Fig. 3.3. Boronia seeds
aril aril
Fig. 3.4. Castor-oil seed
Fig. 3.5. Orchid seed
This organ transmits nutrients from the funicle through the testa into the nucellus. The raphe is usually too small a structure in the mature seed to be easily seen, but in some species of Boronia it is prominent and becomes covered by a glossy, black brittle layer (Figure 3.3). An additional character of the seedcoat that is found in some legume seeds, such as those of Acacia and Senna, is a fine line that is either u-shaped (as in Acacia) or circular (as in Senna) on either side of the seed. This is termed the pleurogram (Greek for ‘writing on the side’). Associated with the seeds of many species are outgrowths from around the micropyle or enlargements of the funicle; these are known as arils. In some Acacia species the funicle encircles the seed and enlarges to form a yellow or red swelling that remains with the seed when it is shed. In the castor-oil seed an oily outgrowth forms around the micropyle in the form of a wart and is techni-
Fig. 3.6. Legume seed
Fig. 3.7. Hakea seed
cally known as the caruncle (Figure 3.4). In the nutmeg family (Myristicaceae) the seed may be entirely covered by a coloured aril which forms the mace of commerce. These arils, or aril-like outgrowths, are generally edible and are therefore important for seed dispersal by insects, birds or mammals. SEED TYPES
The form taken by seeds is legion, but the following are examples of some of the more common forms that are found in Australian plants: Orchidaceae
The seeds of native orchids are minute (Figure 3.5), some weighing no more than 0.004 g. They consist of a thin, transparent and papery testa made up of air-filled cells. Within the testa is a tiny mass of undifferentiated cells (sometimes no more than 10) which form the embryo. 13
Australian Seeds
Orchid seeds are produced in abundance and are so light that they are readily scattered by the wind. Since the seed contains no storage tissue it will only germinate if it lands in the presence of a soil fungus with which it can form a symbiotic relationship.
The following classification is based on the structure of the fruit. However, it should be understood that fruits of similar appearance may be found in families that are not closely related. Simple fruits Dehiscent fruits Acacia, Eucalyptus Indehiscent fruits, dry Asteraceae, Petrophile Indehiscent fruits, fleshy Citrus, Olea, Santalum, Vitis Aggregate fruits Hibbertia, Ranunculus Multiple fruits Ficus, Morinda
Leguminosae
Genera such as Acacia, Hardenbergia and Chorizema have seeds (Figure 3.6) that are usually almost circular or broadly elliptical and bilaterally asymmetrical; the prominent hilum is positioned along their margins, and may be small or may extend along its whole length. The embryo consists primarily of a pair of cotyledons that may so fill the seed that the endosperm is scant or absent. The seedcoat is usually leathery or brittle. Sometimes the funicle is enlarged at the hilum to produce an aril which remains attached to the seed when it is shed. Rutaceae
The seeds of Boronia show considerable variation (Figure 3.3) but a common form is found in B. crenulata. In this species the seed is sub-circular with a deep hilum groove along one of the lateral faces. The raphe, a fleshy tissue, passes to the base of the seed and is often covered by a brittle layer derived from the outer testa. The inner testa is hard and thick, but a circular hole at its base allows the vascular tissue of the raphe to pass into the nucellus. The embryo is small and the bulk of the interior of the seed is occupied by endosperm.
Simple fruits
These are fruits that develop from a single ovary. If the ovary has more than one carpel then these are fused together. Simple dehiscent fruits
The fruits in this category develop from one ovary and the seeds are released by the splitting of the ovary wall, often along the lines of fusion of the carpels, or by the formation of pores in the wall. Common examples are:
•
Legume or pod (Figure 3.8). These terms are used for the fruits of members of the pea family, Leguminosae, such as Acacia, Senna and Hardenbergia. The legume consists of two valves connected along sutures that separate at maturity to release the seeds that formed a row in the pod. In some genera, such as Hardenbergia, the two valves of the ripe legume are elastic and separate explosively, flinging the seeds some distance from the plant.
•
Follicle (Latin for ‘little sack’). A follicle (Figure 3.9) is similar to a legume but usually only splits along one suture. It is sometimes woody. Examples are found in several Proteaceae genera such as Xylomelum, Grevillea and Hakea. The fruit of macadamia is technically a follicle, but is referred to as a nut.
•
Capsule. A capsule (Figure 3.10) is formed from an ovary that consists of two or more carpels. Examples are fruits of Eucalyptus and many other members of the Myrtaceae, of Drosera in the Droseraceae, and of
Proteaceae
The seeds of Grevillea and Hakea (Figure 3.7), and of others in the same family that bear follicles, are relatively large and flattened. The dry, brittle testa is extended on one side or all around the seed to form a membranous wing. The embryo is usually large and the endosperm absent. Such seeds are obviously adapted to dispersal by wind. FRUIT FORMATION
While the seeds are forming, changes are also taking place in the rest of the ovary. The ovary wall swells and undergoes various modifications to form the pericarp or fruit wall. The pericarp may fuse with surrounding organs, or a number of ovaries may fuse together to form a complex structure. The mass of different tissues that forms around the developing seeds is called the fruit. It may consist simply of seeds and the ovary wall, or it may include the perianth and the peduncle of one or of many flowers. 14
Chapter 3 – Seed and fruit structure
Fig. 3.8. Legume (Fabaceae)
Fig. 3.9. Follicle (Hakea)
Fig. 3.11. Siliqua (Brassicaceae)
Calandrinia in the Portulaceae. A special form of capsule is the siliqua, Latin for ‘a pod’ (Figure 3.11), which is the fruit of the cabbage family, the Brassicaceae. Typical Australian examples are Blennodia and Cardamine. The siliqua is made up of two valves. It is similar in appearance to the legume but is divided into two compartments or locules by a septum that runs its length, bearing one or more seeds in each locule. The two valves break away at the base and curl upwards to release the seeds. A siliqua is usually long and slender, but when it is short and broad it is called a silicula. Another common type of capsule is the pyxidium, from the Greek pyxis: ‘a casket’ (Figure 3.12). In this the fruit is often spherical and forms a horizontal ring of weak cells around
Fig. 3.10. Capsule (Calothamnus)
Fig. 3.12. Pyxidium (Trianthema)
the pericarp and eventually the upper portion falls away like a lid. This type of dehiscence is referred to as circumscissile and is found in many families such as the Portulacaceae (Portulaca), Amaranthaceae (some Amaranthus species) and Aizoaceae (Trianthema, Zaleya and Sesuvium). Simple indehiscent fruits, dry
These are fruits that are dry when mature, are formed from one ovary, and do not break open when ripe. Common examples are:
•
Caryopsis. A common type of indehiscent fruit is the caryopsis, a Greek word meaning that it resembles ‘a nut’ or ‘grain’ (Figure 3.13), found only in grasses. 15
Australian Seeds
Fig. 3.13. Caryopsis (a grass)
Fig. 3.14. Achene (Ranunculus)
Fig. 3.15. Achene (Rhodanthe)
(Casuarinaceae) are in fact fruitlets clustered into what is referred to as a cone (in this case a form of multiple fruit). Each female flower is surrounded by a pair of bracteoles; the naked ovary develops a hard pericarp to form a winged nut. This winged nut (or nutlet) is called a samara, a Latin name for ‘the fruit of the elm’ (Figure 3.17).
It is one-seeded and the testa is fused to the pericarp, but the principal distinguishing character is its complex type of embryo.
•
•
16
Achene. Another common type of indehiscent fruit is the achene, a Greek work meaning ‘not gaping’ (Figure 3.14). This is a small one-seeded fruit with a thin or crust-like pericarp. Examples are fruits of Ranunculus and Clematis (Ranunculaceae), Polygonum and Rumex (Polygonaceae) and the daisy family (Asteraceae). Because achenes are usually small, indehiscent and one-seeded, they are commonly referred to as seeds, though in fact they are fruits. The fruits of the Asteraceae are sometimes referred to as cypselas, Greek for ‘a hollow vessel’, a special type of achene (Figure 3.15). In this, the ovary is surrounded by both the fused pericarp and the floral tube. While normally dry, the outer coat may be succulent as in Chrysanthemoides monilifera, in which state it is known as a drupe (see below). It may become modified to bear spines or wings as occurs in some species of Cotula and Brachyscome. Nut. The term nut is used broadly to include the peanut, Arachis hypogaea (Fabaceae), which is a legume, the Brazil nut, Bertholletia excelsa (Lecythidaceae), which is a seed, and the macadamia nut, Macadamia species (Proteaceae), which is a follicle. In the botanical sense a nut is a dry, indehiscent fruit with one seed and a hard, often woody, pericarp. Nuts are found in a number of genera in the Proteaceae, e.g. Stirlingia, Conospermum (Figure 3.16), and Adenanthos. The ‘seeds’ of the she-oaks
Fig. 3.16. Nut (Conospermum)
•
Schizocarp. In the Apiaceae (Xanthosia family) and the Malvaceae (Hisbiscus family) are found a particular type of fruit called a schizocarp, Greek for ‘splitfruit’ (Figure 3.18). It has two or more dry and single-seeded carpels that split away from each other when ripe. The resultant portions are called mericarps, Greek for ‘part-fruits’. Examples are found in Xanthosia, Platysace, and Trachymene (Apiaceae) in which the fruit splits into two mericarps, and in Pavonia and Sida (Malvaceae) in which the fruit splits into many one-seeded mericarps.
Fig. 3.17. Samara (Casuarina)
Fig. 3.18. Schizocarp (Xanthosia)
Chapter 3 – Seed and fruit structure
Fig. 3.19. Drupe (Santalum)
Fig. 3.20. Berry (Solanum)
Fig. 3.21. Syconium (Ficus)
Simple indehiscent fruits, fleshy
Aggregate fruits
In these fruits the outer portion of the pericarp is fleshy or leathery; if formed from an inferior ovary the united pericarp and floral tube are fleshy. Common examples are:
Some flowers have two or more ovaries free from each other. However, the appearance of fruits formed from flowers with free ovaries is little different to the appearance of fruits formed from flowers with free carpels but united by a simple style. These ovaries can form many individual fruits in the one flower. An example is Hibbertia (Dilleniaceae) in which the carpels, when dry, form achenes, and when fleshy, form drupes.
•
•
Drupes (Latin for ‘an over-ripe olive’). These are commonly referred to as stone fruits since they have a woody endocarp (the inner layer of the pericarp) and a fleshy mesocarp (the middle layer of the pericarp). Examples are the fruits of Santalum (sandalwood and quandong) in the Santalaceae (Figure 3.19). Berries. In these fruits the whole pericarp is fleshy or succulent, except for the outer skin, and they can contain one or more seeds. The fruits of Vitis (Vitaceae), the grape, and Solanum (Solanaceae), the tomato (Figure 3.20), are typical. In the Cucurbitaceae are many different forms of berries, technically referred to as pepos (Latin for ‘pumpkin’), that have a hard rind partly formed from the floral tube; examples occur in Cucumis (cucumber), Mukia, and Luffa (vegetable sponge). The Australian Rutaceae also have specialised examples of berries, such as those in the tropical genera Glycosmis and Micromelum where the fruit resembles a very small orange.
Multiple fruits
These fruits are common in commerce but are not prominent in the Australian flora. They are formed from an inflorescence (a cluster of flowers), not a single flower, and therefore combine tissues derived from the ovary and perianth along with tissues derived from the peduncle or receptacle. Well-known examples of multiple fruits are the pineapple, Ananas comosus (Bromeliaceae), and the fig (Figure 3.21), the fruit of Ficus species (Moraceae). In the Australian fig species, numerous small flowers cover the inside of a hollow flask-shaped peduncle that has an opening at the top. It is technically known as a syconium (from the Greek sycon: ‘a fig’). The edible portion is principally the fleshy peduncle while the pips are individual fruitlets or achenes. Another Australian native plant with a multiple fruit is the cheesefruit tree, Morinda citrifolia (Rubiaceae), a native of the Kimberley region. In this fruit the numerous flowers produce one- to four-seeded drupes joined to form a succulent globular mass, the cheesefruit.
17
Australian Seeds
Some Australian fruit types
Simple dehiscent fruits. An Acacia pod (left), a Eucalyptus capsule (centre) and a Xylomelum follicle (right).
Simple indehiscent fruits, dry. A Triodia caryopsis (left), a Leucochrysum cypsela (centre), and a Conospermum nut (right).
Simple indehiscent fruits, fleshy. A Santalum drupe (left), a Solanum berry (centre) and a Myoporum drupe (right).
Multiple fruits. A simple cone of Callitris (left), a Cycas strobilis (centre) and a Ficus synconium (right). 18
CHAPTER 4
Seed biology and ecology David Merritt and Deanna Rokich
SEED ECOLOGY AND GERMINATION
Australian species can be grouped into those that store seeds in the plant canopy and those that release seeds into the soil seedbank. Species that retain their annual production of seeds on the plant in woody, protective fruits in the plant canopy, only releasing them after considerable time, are known as serotinous (or bradysporous) species. Species of the Proteaceae, Myrtaceae and Casuarinaceae are examples of serotinous species. Seed release of serotinous species may occur with the death of the plant or branches supporting the fruits, or following a fire. The serotinous seed component in drier regions of Australia (e.g. the Western Australian kwongan) may contribute 1100 seeds/m2 of soil surface.1 Conversely, in the jarrah (Eucalyptus marginata) forest there is only a limited number of serotinous species (7 seeds/m2). Plants that annually release seeds into the soil seedbank are known as geosporous. Species of the Mimosaceae, Apiaceae, Stylidiaceae and Ericaceae are geosporous. For a plant community to regenerate from seed, the topsoil and canopy seedbanks need to be in a suitable physiological state to germinate and take advantage of narrow windows of opportunity for successful seedling establishment. Seedbanks within the topsoil or canopy may persist for varying periods of time and germinate either simultaneously in response to favourable germination cues such as fire, or intermittently with germination
events spaced over a period of time. Seeds of serotinous species are generally only shed when conditions are favourable for germination and seedling establishment. Therefore, these seeds are usually non-dormant and able to germinate immediately upon release. Seeds of geosporous species are released each year into the soil seedbank and the risks associated with this simultaneous release into an unreliable environment are minimised through accumulation of several seasons worth of dormant seeds. Dormant seeds are those that do not readily germinate when provided with adequate moisture, appropriate temperatures, light and oxygen (for most species). Dormancy is a state which delays seed germination until conditions are more likely to ensure seedling survival and continued reproduction of the species. Disparities between seed viability and germination percentages observed in research studies indicate that seed dormancy is pre-dominant in our flora, but largely confined to geosporous species as the seeds must be able to sense the environmental conditions to time germination for those periods when seedling establishment is likely. Incorporation of dormant seeds into the soil seedbank can be viewed as a ‘bet-hedging’ response to uncertain environmental conditions, such as moisture availability or variability in the frequency, intensity or duration of fire. Delaying seed germination until 19
Australian Seeds
environmental conditions are favourable for establishment ensures seedling survival and continued reproduction of the species in the environment. Seeds must simultaneously sense a number of environmental conditions and time germination and emergence to particular times and habitat locations for successful establishment and survival. Temperature is one of the major drivers of dormancy loss and seed germination. For many Australian species in temperate and Mediterranean climates germination tends to be best at temperatures associated with the winter rainfall period (approximately 15–20°C) and seeds remain dormant at lower or higher temperatures. Maintenance of seed dormancy under high temperatures is particularly important for species of south-western Australia as summer thunder showers can
occur that may stimulate germination of non-dormant seeds but not produce sufficient soil moisture to carry developing seedlings into the winter period of regular rainfall. At present, the understanding of seed dormancy mechanisms and germination requirements of many Australian plants is limited. The inability to germinate seeds of species from many of the dominant plant families (e.g. Cyperaceae, Laxmanniaceae, Dilleniaceae, Ericaceae, Restionaceae and Rutaceae) is a major impediment to conservation, restoration and horticulture. However, it is well established that dormancy blocks or interrupts the germination process by various physical and/or physiological means along the sequence of events from seed imbibition of water to radicle emergence.
A selection of Australian genera reported to have smoke-responsive seeds Acacia*
Calytrix
Hybanthus
Pimelea
Acanthocarpus
Centrolepis
Hydrocotyle*
Pityrodia
Acrotriche
Chieranthera
Hypocalymma
Ptilotus
Actinostrobus
Clematis
Isopogon
Ricinocarpus
Adenanthos*
Codonocarpus
Johnsonia
Rulingia
Agonis
Comesperma
Kennedia*
Scaevola
Agrostocrinum
Conospermum
Lasiopetalum
Sowerbaea*
Allocasuarina*
Conostephium*
Laxmannia
Sphenotoma
Alyxia
Conostylis
Lechenaultia
Stackhousia
Amphipogon
Crassula
Leptomeria
Stirlingia
Andersonia
Cyathochaeta*
Leptospermum
Stylidium
Angianthus
Dianella
Leucopogon
Tersonia
Anigozanthos
Diplolaena
Levenhookia*
Tetrarrhena
Athropodium
Epacris
Lobelia
Tetratheca
Astartea
Exocarpus
Lomandra
Thysanotus
Astroloma
Ghania
Loxocarya
Trachymene*
Austrostipa
Geleznowia
Lysinema
Tripterococcus
Baeckea
Georgeantha
Macropidia
Velleia
Banksia*
Gompholobium*
Myriocephalus
Verticordia
Billardiera
Gonocarpus
Neurachne
Waitzia*
Blancoa
Grevillea
Opercularia*
Xanthorrhoea*
Boronia
Gyrostemon
Orthrosanthus
Xanthosia
Borya
Haemodorum
Patersonia
Bossiaea*
Hakea*
Persoonia
Brunonia
Hibbertia
Petrophile
Burchardia*
Hovea*
Philotheca
Caesia
Hyalosperma*
Phyllanthus*
Note: The smoke response can vary with seed age and dormancy status. * Species that have been found to be smoke-responsive under field conditions, but not in the laboratory. 20
Chapter 4 – Seed biology and ecology
Banksias are typical of serotinous species in Australia.Their seeds are commonly released from the cones following a disturbance event, usually fire.
Seed dormancy is either imposed by the embryo or by the seedcoat or outer coverings, with two basic states of dormancy recognised: primary and secondary dormancy. Primary dormancy is imposed whilst seeds are maturing on the parent plant. Secondary dormancy refers to seeds which are released from primary dormancy after being shed from the parent plant, but then re-enter dormancy owing to unfavourable environmental conditions. Seed dormancy is complex as there are many ways in which the dormancy may be imposed. An understanding of dormancy is necessary to develop reliable germination methods and is the subject of much study around the world. A recent classification system proposes five main ‘classes’ of dormancy based on readily observable seed and embryo characteristics.2 This system has not been applied to many Australian species to date, but it is nevertheless useful for narrowing down the types of treatments which may be successful in alleviating dormancy. One of these classes of dormancy, which has been long recognised in Acacia species (and other Australian legumes) is physical dormancy. Seeds with this form of dormancy possess coverings (seed/fruit coat) that are impermeable to water. A hot water (near-boiling) or dryheat treatment is often applied to allow imbibition and germination of physically dormant species. Alternatively, removing a small section of the seedcoat (using a scalpel or mechanised scarifier) also overcomes this type of dormancy. In nature, the seedcoats are thought to become permeable by repeated daily heating and cooling over many years in the soil seedbank, or owing to the passage of a fire. Once the physical barrier to water
uptake is removed, seeds of physically dormant species germinate rapidly (often within 2–3 days) at appropriate temperatures. Physical dormancy is known to occur within at least 15 plant families, including many families with Australian representatives, such as Anacardiaceae, Bombacaceae, Convolvulaceae, Geraniaceae, Malvaceae, Mimosaceae and Rhamnaceae.3 Another type of dormancy that appears prevalent in Australian seeds is physiological dormancy. This type of dormancy is recognised as the most commonly encountered form of dormancy worldwide, accounting for nearly 65% of all species in which the dormancy type has been documented.4 In seeds with this type of dormancy the embryo must be physiologically ‘cued’ to induce sufficient growth potential to overcome the mechanical resistance to radicle emergence imposed by the surrounding structures (e.g. endosperm, seed or fruit coat). Physiological dormancy has been shown to be overcome by stratification (moist incubation) in warm (> 15°C) or cool temperatures (1–10°C), or a period of dry afterripening prior to incubation. The commonly used plant growth regulator gibberellic acid often promotes germination of physiologically dormant seeds, as does smoke. Seeds of the difficult-to-germinate, woody-fruited Astroloma, Leucopogon, Myoporum and Scaevola have physiological dormancy. Fire is an important control of natural germination events, whether through direct effects of heat in destruction of seed at the soil surface, breaking of physical dormancy in hard-seeded species, or the opening of fruits to release seeds from the canopy seed reserves. 21
Australian Seeds
Some of the most spectacular of Australia’s plants produce seeds that are very difficult to germinate. Clockwise from top left: Astroloma xerophyllum, Boronia fastigiata, Hibbertia subvaginata, Calactasia narragara.
Recurrent fires within Australian ecosystems provide a periodic situation of an open environment with enhanced conditions of moisture, light and nutrients, normally ensuring the survival of germinated seeds, particularly if the fire has occurred immediately prior to winter. Of particular interest is the stimulatory effect of smoke on seed germination. Smoke and aqueous extracts of smoke have been found to enhance seed germination in over 100 genera of Australian plants. The diverse range of smoke responsive species includes representatives of all plant forms, fire responses and seed germination strategies. The use of smoke as a germination tool has increased the total recruitment and species diversity in mine-site restoration, opened up opportunities for horticultural development of species previously found to be difficult to propagate from seed, and assisted in evaluat22
ing soil seedbank dynamics in fire-prone environments. At present it is uncertain how smoke promotes seed germination, but there is evidence that smoke influences the dynamics of plant growth hormones important to germination.5 In Australia, germination responses to light are less well documented. However, light conditions have been shown to influence the germination of arid zone annuals and jarrah forest species. The ability to sense light is well developed in understorey jarrah forest species, where dark conditions are preferred and light inhibition is particularly apparent at higher temperatures. Increased germination percentages in darkness compared to light appears related to the ability of seeds to sense the buried soil environment. Seed burial generally ensures consistent moisture availability and
Chapter 4 – Seed biology and ecology
improved chances of seedling survival, particularly in the Mediterranean-type climate experienced in the jarrah forest and Banksia woodland where rainfall can be light and intermittent. Surface germination would be disadvantageous for subsequent seedling survival in this climate of periodic rainfall, especially under the warmer conditions of the first rains of late Autumn. The ability to sense the buried environment would also be an adaptive advantage in desert or seasonally arid regions where the soil surface is more likely to be moisture deficient. Some species can emerge from quite significant depths. Legume species, for example, have demonstrated an ability to emerge from depths of at least 10 cm, probably an adaptation to collection and burial by ants. Most of the legume species have eliasomes attached to their seeds which are associated with collection, dispersal and burial by ants. Legume seeds are generally relatively large and contain sufficient reserves of energy to allow them to emerge from depth. In contrast, seed burial can negatively affect the ability of seedlings to emerge and establish. Most small-seeded species germinate within the top 1 cm of the soil surface as they do not have sufficient energy reserves to emerge from greater depths. Many of these species are light requiring. Most species of Asteraceae, for example, require light to germinate, despite many of them occurring in arid or semi-arid regions. Moreover, maintenance of dormancy for some species under vegetation canopies that limit light penetration to ground level avoids competition between
emerging seedlings and already established mature plants. When soil disturbance or vegetation clearing increases exposure to light, seed germination is stimulated. The requirement for multiple cues (two or more cues in combination, or applied sequentially) to break seed dormancy is little appreciated in the Australian flora. In certain species, the role of smoke as a germination cue may be ancillary to other mechanisms. Some species, for example, require scarification of the seedcoat and incubation at alternating temperatures in addition to smoke treatment before maximum germination occurs.6 Many Australian species respond more positively to smoke after a period of aging in the soil, or following a number of months dry storage (after ripening), and without both treatments there is no germination. This suggests that physical and/or physiological changes induced by fluctuations in soil temperature and moisture render seeds non-dormant, and that smoke is the final ingredient required to elicit germination. In this regard there is a question over whether smoke is a dormancy breaking agent per se, or more of a germination-stimulating agent that promotes germination after dormancy is lost via another process. Interestingly, when some species are stored in soil, there is a decline in viability by more than 50% in less than one year, but for the remaining viable seed, germination improves in the second year, indicating that a substantial trade-off takes place between viability decline and dormancy release.
A typical scene following a fire in Western Australian kwongan heathland. In this small patch of soil, many of the most difficult to germinate species can be seen emerging, including species of Hibbertia and Ericaceae.
Another post-fire landscape. Many fire-stimulated species are evident, including Anigozanthos, Stirlingia and Tersonia.
23
Australian Seeds
SEED ECOLOGY AND RESTORATION
An understanding of seed ecology is important for effective restoration of degraded landscapes. For some restoration purposes, the topsoil seedbank is an important source of seeds, and for some plant species it may be the only source for establishment in disturbed areas such as post-mined sites. For example, in rehabilitation of post-mined jarrah (Eucalyptus marginata) forest, 72–77% of species which re-establish are derived from the topsoil seedbank,7 which is removed from forest sites prior to mining and subsequently replaced within the same sites during the restoration process. Thus, handled correctly, the topsoil seedbank can be used to successfully revegetate these types of disturbed areas. However, a thorough knowledge of the species composition, abundance and distribution in the topsoil seedbank is first required for setting restoration targets. A unique feature of the kwongan vegetation, north of Perth in Western Australia, is that a large number of species are serotinous. In this plant community, where the majority of species do not store their seeds in the topsoil seedbank, replacement of species to sites requiring restoration is achieved through use of the canopystored seedbank. In these instances, a mulch of the canopy material (containing the serotinous species) is the most important source of seeds in post-disturbed sites within kwongan vegetation, containing 85% of the total germinable seeds, whereas the topsoil seedbank contributes only 13% of the germinable seed.8
Optimising the germination of seeds and the restoration of the full range of species present before disturbance also requires an understanding of seed viability, longevity and dormancy. For germination to be initiated, three conditions must be fulfilled. First, the seed must be viable; that is, the embryo must be alive and capable of germination. Second, any dormancy condition present within the seed must be overcome. Third, the seed must be subjected to appropriate environmental conditions of available water, correct temperature regimes, supply of oxygen and sometimes light. Seeds are at their physiological peak when they reach maturity. Following this point a decline in seed viability occurs, owing to the aging process, and is assumed to continue until death of the seed. The potential longevity of any particular species is determined genetically and some species may live for many decades in the soil or canopy seedbank, whilst others may lose viability within a year of reaching maturity. The importance of seed longevity in the ecological sense can be viewed when observing the survival of a single generation of seeds through many episodes of uncertain environmental conditions. Where a species produces and disperses seeds with minimal longevity (and/or no dormancy mechanisms) into an environment unfavourable for establishment, the new generation of seedlings would be unlikely to survive. However, a species producing seeds with maximum longevity and/or the ability to remain protected in a dormant state, will contribute to the seedbank until favourable cues for dormancy release and germination are experienced, and the likelihood of seedling survival is greatest.
Two examples of the use of smoke in restoration. Smoke can be applied directly to topsoil returned post-mining, or applied to seeds prior to broadcasting in a restoration site. 24
CHAPTER 5
Seed collection in the field Luke Sweedman and Grady Brand
This chapter outlines the main issues that need to be addressed in order to collect seeds in a comprehensive and sustainable manner. The photographs are drawn from a wide range of collection trips in Western Australia and in Africa. The principles associated with seed collecting are applicable to most situations and although some issues, such as the terrain and the climate, will differ, collecting protocols are the same. The primary reasons for collecting seeds, especially the end use of the material, must be clearly understood by the collector as they will influence the degree and rigour of sampling. The storage conditions and the sampling strategies used for collecting seed of rare species are different from those applied to more common species. Collectors may be collecting material needed for restoring degraded lands, or for conserving genetic diversity of species and populations considered endangered or threatened. Equally, they might be harvesting seed from cultivated and wild sources for commercial uses, including forestry, horticulture and sale to the general public, or seeking material for display or study purposes in botanic gardens or other research institutions. Collecting seeds from appropriate plants can ensure the selection of notable forms, and those with inherently desirable characteristics – selecting for salt tolerance, for example. In the majority of cases, seeds provide a good representation of a population and the inherent strengths
and subtleties of a species. However, propagation via seed in a nursery may not exert the same natural selection pressures on a seed batch as in the wild and it must be remembered that not all characteristics are passed on by seeds. Some species of variable flower colour will not produce true to type from seeds. Some forms, such as a prostrate habit, can be of an environmental origin, rather than an inheritable characteristic. And low seed viability or deep, intractable dormancy may limit propagation and storage potential. GENERAL PRINCIPLES FOR COLLECTING SEEDS
Some principles are common to all types of collecting, regardless of the sampling strategies. Correct horticultural technique is essential when collecting seeds to ensure the ongoing health and vigour of the source population. If the resource is well managed and plants are present in reasonable numbers, seeds may be harvested without adverse impacts on the sustainability of the population. Plants should be assessed as to the availability of material and whether collecting is likely to place the population under stress. If the population is wilted, diseased or unhealthy in appearance, it should be left alone. Collectors should try to leave the population in as good a condition as it was when they arrived. Shrubs should be pruned rather than disfigured or lopped. 25
Australian Seeds
A well-organised collecting vehicle with clearly labelled seed bags.
Collecting spinifex seeds, Great Sandy Desert, Western Australia.
Photo: Stephen Scourfield.
Collecting mature Ptilotus fruits. Photo: Stephen Scourfield.
Collecting Combretum collinum seeds in Tanzania.
There are licensing requirements for seed collecting in most Australian States. These may recommend the collection of only 20% of the available seeds from a population at any one time. This is intended as a general guide to help ensure that collecting does not make an undue impact on the long-term survival of the population. Plants should be cut with sharp tools to ensure that wounds are kept to a minimum and to limit the possibilities for fungal damage and facilitating its spread. It is a good practice to disinfect tools between populations in known disease risk areas. Collection of seeds should be done randomly and be representative with respect to ecological variations within 26
Using a pole pruner to collect Euphorbia in Kenya.
the site. For example, if part of a population is growing in a swamp, it may be better to make a separate, representative collection. Unusual forms within a population should be treated as individual collections if this feature is considered noteworthy. Seeds can be gathered from beneath many plants if the seed has matured and dehisced. However, care should be taken since predation can rapidly take place when mature seeds are available to predators. Cut plant material should be placed in calico, hessian or paper bags and tied securely. Avoid the use of plastic bags as they can lead to uneven drying and condensation
Chapter 5 – Seed collection in the field
Collecting Hakea fruits. Plants should be cut with sharp tools.
Using the vehicle as a platform.
Photo: Stephen Scourfield.
Using sheets to collect Acacia seeds, Wheatbelt, Western Australia.
Pouch and bags secured on a belt. Photo: Stephen Scourfield.
problems. Large plastic bins are perfect to place cut material in as the collection is made. These are easily moved around the population and the contents can then be tipped into bags to be processed. Plastic bins are also useful to tap seed into as you collect through a population, especially where the seeds are balanced on the terminal branchlets, for example Olearia and Cratysylis in the Asteraceae family. Drop sheets are also useful for placing around the base of shrubs to collect seeds. The best of these are light canvas sheets used by painters. These are essential for collecting seeds from many acacias. All collections should be labelled with (at the very
Acacia seeds collected on drop cloths in calico bags.
least) a unique field number and preferably a field number, date and the name of the species. Material that is damp should be packed more loosely and placed in a drying environment as soon as possible. Wear appropriate protective clothing and eye protection. Some groups, such as grevilleas, can produce allergic reactions. Use a pouch for secateurs to keep the hands free. Bags can be tucked into a belt around the waist as a temporary storage. Collectors should be careful not to mix species when making a collection. A dense, pure stand is ideal to keep the seedlot free of other species. It is important to focus 27
Australian Seeds
on the targeted species and to ensure you know what it looks like when seeding. Be aware of collecting in areas where there are weed species which may be inadvertently collected as well. A stable platform on the top of a vehicle is ideal for collecting from most trees. Other options for tall species include rope climbing (only to be attempted by those qualified to do so), or pruning of selected branches using saws or pole-pruners.
•
Are the seeds well formed and turgid? If they contain moisture and appear plump, rather than dry and shrivelled, then they are probably good quality. Simply cutting the seed in half is an easy way of making this judgement. Use a sharp blade to cut the seed.
•
Are the persistent fruits from genera such as Allocasuarina, Melaleuca, Calothamnus and other Myrtaceae shrubs older than the last flowering time? For many of these shrubs it is preferable to select material matured from previous seasons. These fruits are usually located towards the centre of the shrub. The capsules can be cut with secateurs to check for the presence of seeds.
•
Is there any evidence of insect damage, such as webbing, frass or holes in the fruits or seeds? If so, it may be necessary to cut the seeds to determine the quality of the material.
•
Are the seeds dehiscing naturally? Seeds should be dry in appearance and in many cases easily displaced by hand. For example, Thryptomene and Verticordia seeds should be easily dislodged when fully ripe. Alternatively, seeds may be fluffy and fall easily from the plant or be blown off by the wind. Wind dispersed species include Gomphrena spp. and many of the Asteraceae, including the common everlastings (Rhodanthe spp.)
•
Finally, is the timing right? For example, trying to collect Acacia, Grevillea and many other genera out of season may provide you with a small amount of seed, but only that which is left over from the main
MAKING THE ASSESSMENT OF THE RIGHT MATERIAL TO COLLECT
A field assessment is critical for making good collections. To determine whether seeds should be collected, the following must be considered:
Chorizema pods ready for collection.
Senna fruits ready for collection. 28
Billardiera fruits dehiscing seeds.
Chapter 5 – Seed collection in the field
Calandrinia flowering in the Gascoyne region,Western Australia.
Calandrinia plants will continue to mature and produce seeds after harvest.
seeding event some time ago. In temperate Australia, many Grevillea species flower in late winter, through to summer. Knowing when the plants flowered means you can estimate when the seed is likely to be ready. Some annual plants will continue to produce seeds even though the plant has been removed from the ground. This is true of many succulent annuals, such as Calandrinia spp. and Portulaca spp. This is also true of the short-lived Lobelia species.
Some specific points for seed collectors to consider:
•
Stay focused on the aims and intentions of the collecting trip.
•
Is the timing right for the species to be collected and do you have accurate locations of good populations?
•
Do you have good knowledge of the target species and what it looks like?
•
Do you have the right vehicle and is it fitted out to provide safe, comfortable travel?
•
Do you have the correct licenses for collecting and for passing through designated lands, for example, Aboriginal lands?
•
Consider your equipment needs: bags, secateurs, pole-pruners, collection books, plant reference books, tags and safety gear.
•
Set goals about how much material you need so as not to waste time collecting too much or too little.
•
Make clear judgements about the material. If it is not mature, then leave it for a later time.
PLANNING A COLLECTION TRIP
Thorough research and planning before leaving on a trip is crucial. Field-based collecting can be an expensive undertaking and it is important to get the maximum benefit from fieldwork. A well-organised programme with realistic targets is the best way of using time effectively. With clear lists of target species, knowledge of their locations, and an awareness of seeding times, the collector stands a good chance of a successful outcome. Collecting may require specialist equipment, such as pole-pruners or a GPS (Global Positioning System), that most seed collectors now find mandatory. If travelling into remote areas you may need a satellite phone to ensure that you are prepared in the case of an accident. If travelling onto certain land you may need a special permit. Locations may require accurate maps and collectors may require meteorological information to check weather forecasts. Field books and all collecting gear needs to be checked before leaving to ensure everything is in good working order.
THE RIGHT VEHICLE
A reliable, well-organised vehicle is a great asset for seed collecting and the better the vehicle is organised, the longer a collector will be able to work comfortably and safely in the field. A small conventional vehicle can be used of course, but the process is made easier if you have
29
Australian Seeds
Seed collecting vehicle, Geita, Tanzania.
Planning what to target, Geita, Tanzania.
The Western Australian Seed Technology Centre collecting vehicle.
Clearly labelled calico bags.
a purpose-designed and accessible work vehicle. A fourwheel-drive vehicle may be essential in rough terrain and remote areas. A good quality four-wheel-drive, with a large opening rear door and a purpose-built roof rack, is ideal. Equipment is easier to get in and out of this type of vehicle and the roof rack can be used as a platform to reach small trees. A large wire box mounted on the roof of the vehicle is ideal for storing seed bags during a collecting trip. This should have a timber cover over it to ensure bags are protected from the direct sunlight and a canvas cover to protect seeds from the rain and dew. This is handy when you are collecting a lot of material and can also be used to dry material that is damp when collected. On trips of several weeks, bags of material may be freighted back when space becomes restricted. Make sure you know
what conditions material will be subjected to while travelling. If the material is travelling overnight inside a truck, this may be fine. However, transport on the back of an open vehicle in the weather for several days would not be suitable. Whether bags are stored outside or inside a vehicle will depend on the size of the collections. If only small amounts of seed are being collected, storing them inside the vehicle is ideal. Collected material should be arranged so it dries evenly.
30
COLLECTION BAGS
Bags made of calico or hessian can be kept rolled in bundles until needed. They need to be kept clean, without remnants of a previous collection, and should be cleaned by brushing off any old seed. If remnant seed cannot be removed the bags should be discarded. They
Chapter 5 – Seed collection in the field
A pure stand of pink everlastings marked for collection.
Pressing specimens or vouchers.
should have two ties on one side to secure the bags. The bags can then be rolled into bundles for storage. Calico is an ideal material for drying as it ‘breathes’ well. Hessian bags are better for larger, woody species such as Banksia and Hakea. Wool bale bags are a useful size for collecting large amounts, and they are easily moved from plant to plant without tearing. These are available from agricultural suppliers. They may be secured by tying at the top using twine. It is important to secure the bags well as seeds can leak out, and be lost over the course of a long trip. Paper bags can be used for smaller quantities and seeds dry well in these. Small bags can be placed in larger hessian bags to keep the collections organised. It is also good practice to check bags periodically to ensure that the tags remain attached and they are tied correctly. Losing a tag will render the contents useless for determining the exact species. Some collectors advocate labelling of bags inside and out. If the tags are lost from the outside then a separate cardboard tag inside can save the collection.
LEGAL CONSIDERATIONS
All States and Territories of Australia have different licensing requirements for collecting seeds. Contact your relevant state conservation authority for guidelines and ensure all appropriate approvals and licences are in place prior to collection. DISEASE CONTROLS
Collecting in a known disease risk area, or where there is a possibility of transmission by water or infected soil, requires care. Vehicles should be washed well, before and after visiting disease risk areas. Collecting in wet areas or during wet weather where pathogens such as dieback are active is not recommended. Where there is evidence of other pathogens (e.g. aerial canker), sterilise secateurs between collections with bleach or methylated spirits. Collectors should check with local authorities wherever they have not previously collected to ensure they are fully aware of the issues that are relevant to an area. 31
Australian Seeds
SAMPLING STRATEGIES
COLLECTING SEEDS OF RARE OR THREATENED FLORA
The following guidelines for sampling seeds will provide material for a range of uses, including restoration of mine sites or of degraded lands, revegetation programs, collecting for propagation and commercial collecting. In all cases correct horticultural techniques should be followed:
Collection from threatened and endangered plant populations is usually only possible by suitably qualified people who have relevant permission and licences. Collecting is generally done to secure small quantities of material for propagation and storage for conservation outcomes. In some instances the population may only contain a handful of individuals and this places the greatest demands on the collector who must be clear about what material to remove and the aims of the collection. Where the population is fewer than 15 individuals, material should be collected from each individual and treated as a separate collection. The location of each individual needs to be mapped and numbered. Where there are more than 15 individuals in a population, material should be collected from at least 10 individuals, up to a maximum of 50. Selection should be random if possible, but material should be collected from various habitats at the population site. Where there are numerous populations, material should be collected from each of them. Five populations should be the total targeted.
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A good sampling number is 10 individuals out of a population of at least 50 individuals. Where possible, this would be a minimum population size from which to collect. Collecting from at least 10 plants should provide a good range of genetic diversity. If there are interesting forms within populations, such as flower colour, collect from these separately. If collecting large amounts of material, choose large populations where many plants can be targeted to reduce the stress on the overall population. Collecting from a large number of plants improves the genetic representation of a sample and is better than collecting a large number of seeds from a small number of plants.
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Accurate records using field books or a field database should be kept to provide details of all collections. When collecting the same species from different areas label separately. If in doubt as to the species identification, take a specimen with the field number and habitat details for identification by a botanist.
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For revegetation programs, collect local provenance wherever possible. This means that material should, ideally, be collected from areas as close to the site being revegetated as possible. If seeds are collected away from the area then the areas should be as close as possible in habitat type to the intended revegetation site. Only use the same species from different areas if there is no alternative. Modern genetic testing is the only precise way of determining exactly the geographic range over which a species may be collected. However, good outcomes are possible by at least following the principle of localised collection. For large revegetation programs, a botanical survey is the best way of determining the key components of the local flora and ensuring a degree of habitat matching between sites. An accurate list of all species, as well as specimens of each should be made. This can also serve as long-term reference material. A collection number ties the voucher, the seed and the records together.
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Chapter 5 – Seed collection in the field
A good specimen for the herbarium.
Attaching numbered tags to specimens. Photo: Stephen Scourfield.
In some cases the individuals in a population should be tested genetically to ensure adequate sampling of the available genetic pool. Precise recording of all details should be entered in an appropriate field book or on computer. Information recorded should include the number of plants in the population, the precise location (a GPS is useful), soil type, rock type, aspect, condition of plants, associated vegetation, threats to the population and collector identification. A herbarium specimen should be taken for species verification.
includes foliage, flowers and fruits where possible. Identification of plant specimens usually relies on flower parts and without these it is considerably more difficult. A field press can be as simple as a telephone book, or two boards, sheets of newspaper and a rope to bind the press. Adjustable nylon luggage ties are ideal. The plant specimen should always have the field number attached. Small jeweller’s tags are most often used to attach the field number to the specimen. It is standard practice for regular collectors to collect a number of vouchers so that duplicate specimens can be lodged with relevant state herbaria. A field record sheet or book with the field number and other details describing the location, latitude and longitude, a description of the colour form and any other information relevant to the collector is important.
RECORDING SEED COLLECTIONS
Records serve the function of being able to tie the collection to a field number, herbarium voucher, and a range of information on that collection. Records are particularly important for unknown specimens and for locating the plants in the future. Each collection should have a field number assigned to the collection with the collector’s initials or other means of identification. For example, LSWE 3456, where LSWE is the collector’s name (in this case Luke Sweedman), and the number is a rolling number of separate collections made. This number is attached to all material collected including seed bags and herbarium specimens, and is noted in field books. Until a species is known reliably in the field it is very important to take a herbarium voucher for species identification. This consists of a piece of plant material best displaying the characteristics of the plant. Ideally this
A collection record on the Botanic Gardens and Parks Authority, Kings Park, database. 33
Australian Seeds
Secateurs. Photo: Stephen Scourfield.
Drop sheets.
Wool bale sacks. 34
Collection bags (calico or hessian). Photo: Stephen Scourfield.
Long-handled parrot-beaked pruners.
Power pole-pruner.
Acacia pods at the stage of dehiscence.
Chapter 5 – Seed collection in the field
Checklist of equipment for collecting Essential equipment:
• • • • • • • • • • • • • •
Secateurs with secure leather pouch Parrot-beaked pruners Small hand-pruning saw A range of calico and hessian bags Tags for specimens and bags Large and small marking pens Record books or collection sheets Target lists, licences and field guides Plant press Hand lens Drop sheets Plastic bins for picking into Gloves Protective sunglasses
Other equipment that may be necessary:
• • • • • •
Power pole-pruners Small chain saw Global Positioning System Wool bale bags Microscope Small dissecting kit for seeds
Seeds collected from the ground must be checked for predation.
Information such as the amount of seeds collected, notes on the size of the population and numbers of plants sampled are also worthwhile. Increasingly, this information is being entered on portable computer systems in the field. EQUIPMENT FOR COLLECTING SEEDS
It is always good practice to purchase the best quality tools. Having the best quality gear will mean that unexpected failures in the field are kept to a minimum. Different tools may be needed depending upon the level of sophistication and the quantity of seeds required. The checklist above is intended as a general guide to those items that are useful and those that are essential for the collector. TIMING OF THE COLLECTION TRIP
Seeds should be collected when mature and at the point of natural dehiscence. At this point, the fruits and seeds are usually becoming dark in colour, material is dry and becoming woody and in many cases seeds are falling from the plant or becoming airborne. However, collection at
this point is not always possible. In many cases some of the material is mature and other material is still developing. When considerable expense has been allotted to a collection programme, material that is less than ideal may need to be collected. Where possible, a majority of the seeds should be mature and often the best time to collect is when, on average, most of the seeds have begun to naturally dehisce, with only a few being marginally ripe and others still green. Seeds of the majority of plant species will not ripen if collected prematurely. In addition, these seeds may be less vigorous. However, seeds of some species will ripen if picked green. Acacias, for example, that are collected green, but with well-developed pods and seeds, will ripen to produce viable seeds. If seeds are very green, and there is no possibility of returning to the population at a later time, then collecting sections of branches with the fruits can improve the chance of getting mature seeds. Ideally, an early visit to the site should be made to gauge the progress of ripening to ensure seeds are mature when they are collected. 35
Australian Seeds
Green Acacia pods.
Collect Allocasuarina fruits by rolling them away from the stems. Photo: Stephen Scourfield.
A field assessment of seeds is critical for ensuring good collections. Seeds should be studied under a field microscope or hand lens. They should be well formed and all appear similar in form and development. A quick cut test on the seeds will ensure there is a well-formed endosperm. This test in the field involves using a sharp blade (such as a scalpel) to cut a sample of seed in half. The contents are checked for a healthy appearance. Check also for the presence of insects in the material. Consider the condition of the population and whether or not making a collection will place the plants under stress. Considering all these factors will not mean spending a lot of time, but it can improve the quality of the collections. Successful collection of seeds is largely based on a good general knowledge of the species accrued over a number of years. Some seeds are easy to collect and are available for collection at any time of the year, for example many Eucalyptus species, particularly in the southern parts of Australia. Conversely, other species are annuals or ephemerals. These plants generally germinate, develop, flower and seed over a period of less than 12 months. For example, some everlasting daisies such as the pink everlasting (Rhodanthe chlorocephala ssp. rosea) can complete their life cycle in as little as four months. For many of these species there is only a small window in which to make a good collection. The timing can be so precise that collectors must know to the day when the seeds will be ready. Perennial shrubs and trees generally have more reliable periods over which seed is available and it is easier to set guidelines for collecting times. Many plants have seeds
36
retained on the plant and therefore seeds can be collected over extended periods, for example many shrubs of the Myrtaceae such as Melaleuca. Some plants, such as Acacia or Kennedia, dehisce over a number of weeks, meaning collecting times can be staggered to suit a programme. Many species will not produce healthy seeds if the rainfall throughout the growing season has been inadequate. Woody shrubs such as Acacia may abort their seeds if conditions are bad. Thus, although general collecting times can be set for a species, given the vagaries and seasonal variation throughout Australia these must be fairly flexible. Maintaining long-term observations of plant populations and variations in seed set from year to year will improve decision-making on when seeds are best collected. The collecting season is often based upon a number of issues, such as what species are required, when they are flowering, the areas in which these species grow and the local climatic conditions (particularly rainfall and temperature). Visiting an area a number of times throughout the collecting season allows fine-tuning of collection times. On the first visit, when the plants are in flower, herbarium specimens can be taken for species identification. The next site visit may be to collect seeds from those species that set seeds. Finally, a third visit may be made in summer to collect seeds from late fruiting species. Each time you visit an area you continue to build a picture of what different species are doing at different times of the year. This develops skills in observation and timing and increases the chances of making a successful collection.
Chapter 5 – Seed collection in the field
The Canning Stock Route after a fire event has stimulated growth.
Ideal rains trigger mass flowering in the everlasting country, Yalgoo, Western Australia.
Road verge disturbance often stimulates germination.
Balaustion pulcherrimum germinating after disturbance.
CUES FOR UNUSUAL SEEDING EPISODES
Fires
Disturbance opportunists
Fires can have a major effect on the flowering of many Australian plant species. Fire provides the cue for stimulating germination and growth, often resulting in spectacular flowering events, and also triggers the germination of disturbance opportunists. These species can produce masses of seeds as early colonisers of the burnt site. Since fires can be very irregular events, many of these species use post-fire growth to build seed reserves in the soil seedbank. Some of Australia’s rarest plants rely on fire events to germinate. For example, Eremophila racemosa germinates in large numbers following fires the previous year, and then it declines and returns to the soil seedbank to await another fire. Another example is the rare, small
Disturbance opportunists are those species that are only found in numbers following a major disturbance event. This may be fire, land clearing, or, as may have occurred in the past, disturbance by large numbers of ground digging marsupials. Once disturbed, these plants often grow rapidly and are prolific seeders under ideal conditions. Disturbance opportunists are early colonisers linked to nutrient regimes following disturbance events and may be absent from the flora for long periods of time. However, the seeds remain in the soil seedbank, often for long periods.
37
Australian Seeds
Bushland can tolerate fires and smoke stimulates the germination of seeds, Black Point, Western Australia.
Glishrocaryon and Dampiera species flower prolifically in response to fire, Hyden, Western Australia.
Precipitation events (annuals and ephemerals)
Eucalyptus sepulcralis in the Fitzgerald River National Park, Western Australia.
herb Sowerbaea multicaulis. It was collected in 1931, and again in 1964, but it was then not seen again until road grading in the Southern Cross area of Western Australia in the early 1990s and following large fires in 1993. Resprouting species, such as many of the eucalypts, may take many years following a fire to begin seed production. In particular, if fire is followed by poor rainfall in semi-arid country, seeds can be rendered unavailable to the collector for a decade or longer. For example, populations of Eucalyptus sepulcralis, an endemic species from Western Australia, were burnt completely in 1989 and did not sufficiently recover to produce fruits and seeds for collection until 2000.
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From many seasons of observation, it is clear that many species have their own window or ideal conditions which, when met, results in remarkable flowering displays. This most often follows rainfall episodes, given that much of the arid interior of Australia is linked to a pattern of cyclonic events. Rain is often infrequent, intense and occasionally flooding. As a result, large tracts of the semi-arid parts of Australia have seasonal events dominated by groups of annuals such as Rhodanthe spp. and Ptilotus spp. Good years in the Pilbara can see Ptilotus helipteroides dominant at the expense of other species. In especially good seasons Ptilotus exaltatus and Swainsona formosa can dominate together. In the tropical Kimberley region, Gomphrena spp. are often prevalent. These short-lived species will dominate the perennial shrublands in good rainfall seasons; at other times they do not appear. It is apparent that different species are triggered by unique seasonal conditions. For example, Rhodanthe chlorocephala subsp. splendida requires substantial and consistent amounts of rainfall to reach peak flowering. Schoenia macivorii, a beautiful everlasting, also requires large amounts of rainfall to emerge in abundance. In particular years Rhodanthe sterilescens can completely dominate in regions such as Carnegie in Western Australia, and other species are not seen. Some species are very site-specific and do not range over large areas and may never occur in large numbers. Such species include Rhodanthe oppositifiolia subsp. ornata in Shark Bay in Western Australia, Haptotrichion colwillii from the
Chapter 5 – Seed collection in the field
Rhodanthe sterilescens growing at the exclusion of all other annuals, Carnegie, Western Australia.
upper Murchison region in Western Australia, and Rhodanthe rubella from the Western Australian Goldfields. In an ideal season, some of the more obscure species may be scattered within larger populations and are difficult to detect. For example, Rhodanthe chlorocephala subsp. cremea was only collected from Shark Bay when it was noticed that within large populations of Rhodanthe chlorocephala subsp. splendida, there was a different group of plants, fewer in number, but nonetheless distinct. Therefore, the seed collector may need to be astute in looking beyond the obvious characters and seeing the unusual and less abundant species. Other ephemerals are less reliant on consistent, seasonal rainfall, but more reliant on unusual seasonal conditions. For example, Velleia spp. and annual Goodenia spp. appear to tolerate drier conditions and intermittent rainfall more successfully than Rhodanthe spp. DEFINING A GOOD SEASON FOR FLOWERING AND SEEDING
Moist, autumn conditions followed by good winter rains produce ideal conditions for annual displays in temperate Australia. Major flower displays can be seen in the semi-arid mulga country of Western Australia. These ideal conditions are created in April when mid-level disturbances merge with strong winter frontal systems. When these conditions are followed by regular, soaking rains throughout the growing season, a good season is assured. Peak flowering occurs in August or early September. Huge quantities of seeds and vegetative material can be produced in these displays.
Brunonia australis grows commonly with Waitzia species, Wiluna, Western Australia.
Goodenia dominating around Mt Augustus, Western Australia.
Intermittent rains from inconsistent, weak frontal systems, or late rains in early winter result in small ephemeral plants with few flowers and seeds. Good, oneoff seasons that produce large displays of ephemerals are not necessarily ideal conditions for flowering and seeding in trees and shrubs. This will not translate into good seed production unless there are consecutive years with good rainfall. SEED PREDATION IN WILD STANDS
In some populations, insects may heavily predate certain species, with the type and level of predation contingent on a number of habitat variables. Predation is often more common in isolated or fragmented bushland areas where 39
Australian Seeds
A great everlasting season.
A bumper year for shrubs and annuals on the Canning Stock Route.
populations have already significantly declined. The collector may need to evaluate different populations in different areas before determining if good quality seeds have been secured. Some of the most highly predated genera are Acacia, Banksia and Patersonia.
acuminatum and Anigozanthos manglesii can be genetically distinct at distances of a few kilometres. Therefore, several collections across the range of a species will better represent the changes at a species level overall. Keep these collections separate and use those that are closest to the site being restored. Careful observations and visits over a number of seasons, particularly in spring and summer, to potential collection sites is a good strategy and will mean that collections can be made across a full range of species. Six to eight weeks after flowering Acacia species are likely to have ripening seeds, but it may be up to three months before they reach full maturity. For other plants, such as the everlastings, seeds will be available in the last two weeks of September, in a good season, in Western Australia. Precise seeding times are difficult to provide for those species that drop seed and frequently visiting sites is the best tactic for getting it right.
IMPLICATIONS FOR THE COLLECTOR
The collector needs to consider all of the above factors to successfully collect a complete range of species. It may not be necessary to gauge all the issues if the object is to collect only a few species, but with knowledge of these interactions a collector can make better judgements about strategies for collecting. This will in turn lead to improved cost efficiencies. When a species occurs across a wide habitat range, then the issue of provenance is worth considering. It has been shown genetically that some species differ significantly across a small range. For example, Santalum
40
CHAPTER 6
Drying and cleaning seeds after collection Luke Sweedman
The handling of seeds following collection involves several steps: the treatment and storage of collected material while still in the field, drying the material before cleaning, and cleaning itself. Collection and storage practices in the field can influence seed viability and longevity in the store, and it is counter-productive if successful collecting practices are followed by poor post-harvest management. This chapter details appropriate methods for drying seeds in the field after collection, prior to cleaning back at the seed storage facility. It also provides an overview of common seed cleaning methods and the equipment used. DRYING
Seeds collected in the field will naturally be at a range of stages of maturity since fruits tend to ripen and mature over the plant at slightly different times. When making a collection, the aim is for an average maturity, whereby the majority of the material collected is mature. By drying correctly, all the seeds are subjected to similar conditions. Careless handling at this early, critical stage, can impact on the overall quality of the collection. In general, mature material (that is, material at the time of natural dehiscence), should be dried evenly and slowly from the point of collection onwards. A cool, mild, even temperature and a dry environment with good ventilation are the best conditions for drying seeds of the
majority of species. These conditions will ensure the immature seeds continue to reach full maturity and the balance of the collection begins to dry evenly for storage and maximum longevity. Cool and dry conditions are not common in an Australian summer, but the humidity is often low, and by drying in the shade, avoiding direct sun, good results are obtained. Where the humidity tends to be high during the day, in tropical areas, for example, it is important to get seeds to an air-conditioned environment as quickly as possible. This is especially important for seeds destined for long-term storage, and slow reduction of moisture content may need to be achieved by using a purpose-built drying room. Removal of moisture using a desiccant in a controlled environment is also a good option if humidity is high. In some instances, seeds that are very immature can be held at higher moisture levels until mature. This may be in a loosely tied plastic bag or an enclosed container, opened daily to ensure air circulation. If the seeds are too damp and there is evidence of rotting, they should be dried and then returned to the container. These practices may be necessary when a species is harvested early to coincide with a window of opportunity for collecting the species. Many seed collections are not being made for longterm storage, so drying and subsequent storage do not need to be rigorous or complex. Much can be done to 41
Australian Seeds
Material transported from the field, Great Sandy Desert, Western Australia.
Seeds being dried in a well-aerated covered area, Geita, Tanzania.
achieve good outcomes without expensive facilities, by simply following good practices in managing a seed collection. It is important to be aware of the conditions in which material is harvested. In many parts of Australia, collection takes place in hot and dry conditions. Under these conditions seeds should be kept as cool as possible, well ventilated, and not exposed to strong, direct sun or stored in overheated conditions within a vehicle. If the weather is cold and wet, it is important to place the seeds in a dry, perhaps air-conditioned, environment. If the seeds are very damp, they can be laid out thinly on newspaper and dried in the shade or in a well-ventilated room. If the conditions are humid and damp, material may need to be stored inside a well-protected environment out of 42
Seeds frozen in glass jars, Cordoba, Spain.
the weather such as an air-conditioned room. Where seeds are being collected in high humidity environments, it may be possible to use boxes containing desiccants such as silica gel or even rice to help remove moisture from the seeds. If the sun is being used to dry seeds during the day it is advisable to store them inside or in sealed containers at night to maximise the drying potential during the day. Humidity rises at night and by protecting the seeds you will reduce moisture fluctuations in the seeds. If a collecting trip is long, arrangements may need to be made to get material back to the base earlier than planned so it can be spread out and dried correctly. When seeds are being collected, ensure the bags are not packed too densely with seed and other plant material. Bags should be stored in a protected place, such as a vehicle, with good aeration and air movement, if possible. A wire basket on top of the collecting vehicle can be very useful for drying when collecting large amounts of seeds. Protecting the bags from the direct sun can be achieved by placing layers of hessian bags or shade cloth over them. If conditions are very hot (40°C), keeping bags inside the vehicle may be best. When an opportunity arises to dry material outside, place all bags in a shady place on a tarpaulin or similar. Placing the bags under a vehicle may also be an option if conditions are hot and sunny. Remember that as the temperature falls the humidity rises so it is important to keep bags inside the vehicle overnight, or at least place them on a canvas tarpaulin and cover them to minimise moisture absorption. The moisture content of high value seeds should be regularly monitored where possible. The reason we do
Chapter 6 – Drying and cleaning seeds after collection
Seeds loosely stored in wool bale sacks.
Bags should ‘breathe’ and the seeds monitored to ensure they are not overheating.
this is to ensure that they are drying evenly. Because seeds are permeable, they respond to changes in relative humidity from day to day. Humid weather means more moisture is in the air, and seeds will absorb some of this moisture. For precise measurement of relative humidity moisture in the field there are accurate hygrometers available. However, these are expensive and probably only necessary for long-term conservation collections. FIELD TIPS Do
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• • •
Collect at the natural dispersal time, in spite of the issues concerning relative humidity and temperature after collection. The quality of the seed when it is collected is paramount.
Acacia seeds at the ideal stage for collection.
Collect seeds when mature and keep in a cool, protected and well-ventilated environment.
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Rotate bags on the top of the vehicle, or wherever they are stored, to ensure even field drying.
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Knead the bags to ensure the material is not stuck together, or open and redistribute.
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Regularly check material by opening bags to monitor moisture and drying.
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Try to transfer collections back to the storage facility as soon as is possible given the time of the collection trip.
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Dry material of succulents separately. This material should be placed in drying trays as soon as you return from the field.
Use air-conditioning where available. Take steps to protect the seeds from fluctuating climatic conditions by storing in a protected environment, for example during the night or in the morning when dew is prevalent.
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Protect from direct sun by covering during the day and storing inside at night.
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Ensure damp or wet material is not placed with other bags where it can encourage mould or rotting. Place material thinly on newspaper and dry as soon as possible.
43
Australian Seeds
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Tie labels securely (possibly inside and out) and check for torn bags.
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Tie coloured tape or some other form of marking on bags that contain spiky or sharp fruits such as Dryandra or Solanum to warn the collector when handling bags.
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Manage high value conservation collections with extra care. This may mean monitoring the relative humidity in the field before delivering to a purposebuilt drying room.
Don’t
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Fill bags with excessive amounts of vegetative material while collecting.
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Expose seeds to extremes of temperature or wildly fluctuating humidity regimes.
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Subject seeds to physical damage.
Markhamia seeds dropping from pods in an igloo, Geita, Tanzania.
Subject seeds to insect predation after collection.
Through simple good practices, the chances of keeping seeds viable until needed are considerably improved. If seed is to be used as soon as it is collected, it is still very important not to waste the resource by mismanaging collections, which are expensive to make. Conversely, if the seed is to be stored as part of a longer term conservation strategy, the chances of fulfilling these requirements may be dramatically reduced if collections are not managed correctly. DRYING ON YOUR RETURN
All bags should be placed in a drying area as soon as possible on return from the field. The ideal drying room is considered by many to be a room with a relative humidity of 15–20%, and a temperature of 15–20°C. Most seeds collected at the right stage of maturity can be placed in a room such as this immediately. If seeds are not intended for long-term storage, then many facilities with a simpler structure will still suffice. If seeds are collected when damp they should be dried in a wellventilated area prior to being placed in the drying room. Seeds should be placed in thin layers and turned regularly to ensure even drying. It is important that material is not left in hot, poorly ventilated areas with high or greatly varying humidity as this can reduce seed viability. Some species are particularly susceptible to rotting. Many Asteraceae, for exam44
Seeds from around the world in a drying room at the Millennium Seed Bank Project, Wakehurst Place, UK.
ple, rot easily if left moist in bags. Very hot summer conditions can also compost some seeds (Rhodanthe species, for example). If seeds are collected in calico bags, they can be dried in these, or alternatively spread out in trays or on a concrete floor. Ensure the material is aerated by turning regularly and evenly, and monitor the drying. Succulent plants should be placed in cool, dry conditions for the seeds to continue to mature and some species, such as Calandrinia and Lobelia, can take four to six weeks to dry. To avoid confusion, be careful not to dry two similar seedlots, for example two species of Melaleuca, next to each other. Ensure the appropriate label remains with the
Chapter 6 – Drying and cleaning seeds after collection
Allocasuarina seeds falling from fruits.
Seed drying on racks in a well-ventilated position, Kings Park and Botanic Garden, Perth, Western Australia.
Seeds being sun-dried, Geita, Tanzania.
A well-ventilated polythene igloo, Geita, Tanzania.
seedlot during drying. Begin cleaning the seed as soon as possible, as this aids the drying process. If the seed was collected at an appropriate time, much of it may be ready to clean immediately. Some species, particularly those of the Myrtaceae, may require a few days or a few weeks for the valves to fully open and release the seeds.
would be better placed in air-conditioned conditions. Drying sheds are a good means of protecting seeds from rain and condensation. Seeds dry well when laid out thinly on trays.
DRYING SYSTEMS Sheds with drying racks
These are often made of timber or wire and rely on the airflow through the shed and the ambient conditions to dry seeds. Well-aerated, semi-open sheds are ideal. These work well in dry climates. Collections in tropical regions
Polythene igloos
These need to be very well aerated as heat build-up can be a problem, especially during summer months. Aeration can be achieved using efficient extractor fans. The igloos should have concrete floors to reduce the build-up of moisture from condensation. Igloos are often used for large collections, as material can be spread out and a fork used to turn and aerate the collections. Material is kept in 45
Australian Seeds
these houses until the seeds have fallen from the fruits. Once this has occurred the seeds should be removed and placed in a storage room, or packaged and stored. Material left in igloos at night will almost certainly be affected by condensation. This should be avoided. In general, igloo drying is not recommended where material is exposed to hot conditions. However, igloos are a relatively cheap and fast method of processing large amounts of seeds and for this reason they are commonly used. With more thoughtful design, especially in the extraction of hot air, they could become more efficient. Air-conditioned rooms
Air-conditioned rooms can be an effective way of drying and storing seeds. They are generally low in humidity and provide a controlled, cool temperature. They are a relatively low cost means for storage if no other facilities are available, and are most suitable for storing material that is required for short-term use. Purpose-built low humidity drying rooms
With this type of room, seeds are dried to low moisture levels under tightly controlled conditions, usually for long-term storage. These offer the best method of reducing moisture within the seed in a controlled and measurable way and are employed by larger seedbanks dealing with long-term conservation. CLEANING SEEDS
Seed is cleaned to reduce the bulk of the collection and to aid in uniform drying. Ideally, seeds should be made free
Air-conditioned storage room, Geita, Tanzania. 46
Seed drying room at the Millennium Seed Bank Project, Wakehurst Place, UK.
of impurities such as stems, sticks and leaves. Most collecting involves harvesting seeds from the fruits and fruits often contain frass or chaff, which can be either a result of aborted seeds, or merely packing around the seeds. Fruits vary in their timing and ease of releasing the seeds. Many seeds can be extracted easily and simply by merely sieving the fruits. Other seeds need tedious and time-consuming techniques to extract seeds successfully. The key to successful cleaning is to consider what type of fruit the seed comes from and what the actual seed looks like. Sometimes this can be confusing, as some frass looks similar to seed. However, a quick cut test will establish the true seed. From this point, the aim is to develop as easily as possible a method to remove the seed without all the frass or chaff. It may not always be possible to clean material to pure seed. Some species have chaff or packaging that is difficult to separate and it may not be cost effective to do so. In some cases it may be appropriate to clean the bulk of the material from the seed and then store or sow the seed with a percentage of chaff. Species of Asteraceae, for example, are cleaned to pure seed for commercial sale but this standard may not be required for many purposes. Therefore, always consider how clean you really need the material and what labour input you are prepared to make to achieve the outcome. Seeds can be contract cleaned if the correct machinery is not available. This is also a very practical option if you have large amounts of material that is difficult to clean, or when material is allergenic, such as kangaroo paws (Anigozanthos spp.).
Chapter 6 – Drying and cleaning seeds after collection
Some seed is ready to clean as it is collected.
Large pods cleaned in the field.
GENERAL CLEANING TIPS
Checklist of equipment for cleaning
•
Essential equipment:
Examine the seeds under a hand lens or microscope to determine what they look like and check their condition at all stages of the cleaning process. This will ensure that seeds are not being damaged unduly. When you are sure what the seeds look like, plan how to clean them without losing too much seed and without damaging the seeds.
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Ensure that the valves of persistent fruits have opened and dropped all seed.
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Small quantities of seeds can be separated by hand using sieves and winnowing.
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It may be counter-productive to persist in cleaning seed if there are only very small particles remaining. For species such as Melaleuca (where seed can be only 0.5 mm in diameter) some frass may be stored with the seed.
• • • •
• • • • • •
Secateurs Sets of various sized sieves Trays (e.g. galvanised trays that can be used to lay out material) Large plastic bins and other smaller plastic containers (used to separate parts of the collection as it goes through the cleaning process) Gloves, safety masks and glasses Marking pens and labels Cleaning equipment, including vacuum cleaners and brooms Set of funnels Microscope and dissection kit Bailing fork
Other equipment that may be necessary:
• • •
Compressed air for cleaning machinery Aspirated blower Threshing machine
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Operating purpose-built machines requires training to ensure they are used to their full potential.
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Keep the work area clean by using vacuum cleaners or compressed air. Clean the machinery and sieves after each different species.
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When using threshers and blowers, it is imperative that the plant material associated with the seeds is dry and brittle, as the machines will work more effectively.
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Keep all stages of the processed material until you have finished. In this way you are less likely to inadvertently throw away seed.
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Be careful to clean individual species separately if possible to reduce the opportunity of mixing collec-
•
The least damage to the seeds will be done by the gentlest means of cleaning. Threshers can damage a
tions. For example, if using machinery, don’t clean one Melaleuca species together with another Melaleuca species.
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Australian Seeds
percentage of seeds and this is a consideration with long-term conservation collections. For small, highvalue seedlots it may be preferable to clean using simple equipment. Gloves and sieves, or wooden blocks and a non-slip surface may suffice in cleaning a collection at a more controllable level.
•
Good collecting can make the cleaning task much easier, so avoid gathering too much foliage when the collection is made.
THE CLEANING AREA
An ideal cleaning area consists of the following features:
•
It should be a large space, well ventilated and airconditioned.
•
It should be close to drying and storage areas, but not share the same space. This makes it easier to control rodents as well as facilitate a flow through system.
•
It should have plenty of power outlets and very good lighting.
•
The floor should be concrete, ideally with no skirting boards or areas that are difficult to clean.
•
Health and safety approved extraction equipment should be fitted for dust removal.
•
Machinery should be installed correctly with consideration as to ergonomic and safety issues.
•
Safety masks, glasses and hearing protection should be available as required.
The cleaning area at the mine site, Geita, Tanzania. 48
CLEANING MACHINERY
There is a large range of equipment available and many types of machinery can be adapted to seed cleaning. Some traditional farming implements have been adapted for cleaning seed. For example, the multi-crop harvester is useful for separating large amounts of trash from seed and is useful for large collections of everlastings. This type of machine provides a threshing action that breaks the stems and heads apart, as well as a rough screen that separates the seeds and petals. Homemade threshers and cement mixers have also been used for seed cleaning. However, the sophistication of the facility should match the needs of the operator and in many cases machinery is not required. Sieves can be used to do the majority of cleaning for smaller amounts of material. Some genera are more complicated to clean and can require a combination of methods. This may be sieving and winnowing (either windblown or using mechanical air-blowers), or threshing and then sieving. Sieves
The most useful item in the seed cleaning shed is a set of hand sieves of various sizes. It is best to have two sets, a small set with very fine screens for removing small particles, and a large set of approximately 300 mm diameter to quickly separate stems and large fruits. In many cases, using hand sieves, as well as utilising the wind in a winnowing action to blow off the lighter fragments, can clean seed. In these cases cleaning is simply a matter of separating the seeds from the chaff or frass. A large range of genera can be cleaned to varying degrees this way, including Acacia, Agonis, Angophora, Beaufortia, Bossiaea,
Seed cleaning area, Nindethana Seeds, Albany,Western Australia.
Chapter 6 – Drying and cleaning seeds after collection
Callistemon, Calothamnus, Corymbia, Daviesia, Eremaea, Eucalyptus, Grevillea, Hakeas, Helichrysum, Kunzea, Lasiopetalum, Leptospermum, Melaleuca, Regelia, Rhodanthe, Thomasia and Xylomelum. Threshing machines
Threshing machines are commonly used to break up plant material, and often provide a precursor to the action of air screen cleaners. They are especially useful for material where the seed is enclosed at the base of the flower and the seeds are held tightly within the dead or dying heads, for example, Anigozanthos, Dodonaea, Gomphrena, Ptilotus and Rhodanthe. Some other species that can be sieved but are easier to clean using a thresher include Acacia, Bossiaea, Daviesia and Senna. In general, pods and pea fruits are much easier to clean with a thresher. Threshing material in machines must be done with care. Ensure that all the foliage to be separated is completely dry. It is very easy to damage or even destroy soft-coated species. An entire seedlot can be destroyed in seconds without diligence in assessing the seedlot throughout the process. Aspirated blower
The aspirated blower is an essential piece of machinery
for most cleaning sheds. It works better when some precleaning has been done using hand sieves or a rotary screen to reduce the bulk of the material. The machine is excellent for winnowing insect-damaged or empty seeds from a collection, and can be used for separating lighter chaff or other materials (such as petals) from the seed. The seed is passed over various screens and sorted based
Cleaning area, Millennium Seed Bank Project, Wakehurst Place, UK. Note the large range of small sieves.
Cleaning area with dust extraction equipment, Kings Park and Botanic Garden, Perth,Western Australia.
on size, and a blower propels the lighter material away from the seed. The screens are available in different sizes. This machine is ideal for a large range of material. Everlastings and other daisies that have petals are cleaned very effectively using this machine. The groups of seeds initially cleaned by the thresher are often run through this machine for final cleaning. Species which may be cleaned include Anigozanthos, Gomphrena, Ptilotus, Trachymene, Velleia and most Asteraceae. It can also be used for species that have good-sized seeds with bulk material to be removed, such as Acacia, Swainsona and Hibiscus.
A large set of sieves is essential for cleaning, Geita, Tanzania.
49
Australian Seeds
Thresher in cleaning area, Geita, Tanzania.
A small aspirated blower, Nindethana Seeds, Albany, Western Australia.
Gravity table/gravity separator
Conical or spiral/centrifugal separator
The gravity table separates small fragments of stems, stalks and leaves from the pure seeds. It is a rectangular, reciprocating inclined deck, covered in cloth or steel mesh, through which air is passed. Seed material is dropped into one corner and the reciprocating motion of the deck causes the material to become fluid, spreading across the suspended airflow. By adjusting the frequency, pitch and airflow, material of a higher density or specific gravity falls to the low side of the deck, whereas the lower density material travels to the top. The seed marches up the table as the chaff drops down the table. This is very effective for light seeds and overcomes the problem of extracting trash the same size as the seed. This machine is ideal for cleaning all the impurities from seedlots of everlastings.
These machines consist of a tall, steeply curving track on which material is dropped. Spheroid material or particles of a higher specific gravity move to the outside of the spiral and lighter fractions move to the inside. A series of gates or ducts at the bottom of the spiral allows material to be separated. The seed rolls down on the same trajectory while rubbish moves at a different rate. The result is that the different weights are separated. They are very useful for Acacia, Senna and Boronia. Zig-zag aspirator
Seeds are dropped in a hopper at the side and a variable speed control vibrates seeds into a chute. A variable suction from the top of the chute extracts lighter fragments from the collection. This machine is ideal for separating out lighter weights of material from seeds. Rotary screen or trommel
This machine is used for roughly separating seed from dried foliage. The seed and foliage are rolled in a long, circular wire cage containing different sized meshes. As the material rolls forward, the seed portion drops through the metal screens while the rubbish slides forward and out. CLEANING TIPS FOR UNUSUAL GENERA Banksia
Gravity table, Nindethana Seeds, Albany, Western Australia. 50
Banksia fruits have persistent cones with valves (follicles) which remain closed, even after being picked and dried. The methods that may be used to extract the seeds are as follows:
Chapter 6 – Drying and cleaning seeds after collection
Centrifugal separator, Nindethana Seeds, Albany, Western Australia.
Zig-zag separator, Millennium Seed Bank Project, Wakehurst Place, UK.
Method 1 – burning
•
Using a cement mixer, place all cones in and begin revolving.
• •
•
Introduce heat via a gas-driven hand piece or torch and set alight combustible material.
Dryandra
•
Keep the heat up for several minutes, then stop and examine the valves.
•
As valves begin opening, tip the contents of the mixer into a water container. Ensure the valves are actually opening as they can begin to open and then stall unless continuous heat is applied.
•
Drain quickly and place in fine wire trays. Keep warm in the sun, an igloo or oven at 35°C.
•
Knock out the seeds from the cones and sieve to clean off the wings.
Temperatures up to 35°C are ideal. Cones can take several weeks to fully open.
Use gloves to remove seed follicles from the foliage. The follicles will open under warm conditions in a drying oven. Lightly frying the follicles in a hot pan will also release the seed. Sieve to remove dust. Alternate wetting and drying will also release seeds (as for banksias).
Method 2 – non-burning
•
Alternate wetting and drying in a warm hothouse will slowly release seeds.
• • •
Wet fruits sparingly. Lay out on wire racks to support cones. Collect seeds as they fall onto shadecloth below.
Rotary screen, Nindethana Seeds, Albany, Western Australia. 51
Australian Seeds
Seeds with fleshy coatings
Some berries and drupes that have a fleshy covering need to be soaked and mashed to remove this outer coating. In many cases, this outer fleshy coat can be rubbed off using a sieve. PEST AND DISEASES
Most pest problems will be in the bags you bring back, rather than occurring after returning to the store, and it is important to check all seedlots thoroughly as they are being cleaned. Some fruits are particularly prone to insect damage (e.g. banksias). Where natural populations are heavily disturbed, for example, on the Western Australian Swan Coastal Plain with species such as Hardenbergia, Hovea and Patersonia, pest attack seems to be at its worst. Many grubs eat hard-seeded species and acacias can be badly affected. If the seeds are treated correctly then they can be kept after the infestation. To check for pest damage, lay uncleaned seeds out in trays or on a concrete floor and carefully examine for insects, holes or other signs of predation. If large numbers of seeds have holes through them they should be discarded. If the infection is minor a spray with an aerosol Pyrethrum should solve the problem. In the past, seeds were often treated with chemicals, regardless of whether they were infected or not. The current thinking is that unless a seedlot has visible signs of damage, then it is better to leave it untreated. All seeds at the Western Australian Seed Technology Centre at Kings Park and Botanic Garden were, in the past, treated with chemicals. Seeds were placed in glass jars with Dryacide, a siliceous clay that dries out insects. These techniques are no longer used as most seeds are frozen. Any seedlot that has been treated should carry a warning, especially with Dryacide, as it can be unsafe if inhaled. Carbon dioxide has been used effectively to fumigate seeds in plastic, impermeable bags, and also used to be a standard practice for collections before freezing temperatures were used to store seeds. Carbon dioxide is a relatively non-toxic way of killing insects, working by excluding oxygen from the bags. However, its action is not immediate and it can take
52
Banksia fruits with valves fully open after burning.
a fortnight to kill all insects, so that if there is active insect attack, the damage may continue for some time. Freezing is a very effective way of preventing insect damage, and can also be used for killing insects from plant specimens entering herbaria. Rats and other rodents can be a serious problem wherever there is plant material, especially seeds. Rats will eat through calico bags and are particularly active after the summer, as they look for places to breed. Bait regularly. SAFETY CONSIDERATIONS
There are inherent dangers when you are operating machinery or using insecticides. Secateurs, saws and other collecting tools need to be handled with care at all times. A significant problem associated with cleaning seed is dust. The cleaning area needs to be well ventilated with proper extraction equipment fitted. Respirators and dust masks should be used, as the fine particles from some species of plants are highly irritating. For example, kangaroo paws (Anigozanthos spp.) are irritating and wearing overalls as well as a respirator is recommended. It is important to use gloves when handling plants with spiky or sticky foliage. Safety glasses and earplugs should also be used when appropriate.
CHAPTER 7
Seed storage and testing David Merritt
SEED STORAGE CHARACTERISTICS
A basic understanding of the factors influencing seed longevity, the storage requirements of different species, and the methods used to test seed viability is fundamental to successful seedbanking. Although long-term storage is not always the role of a seedbank, it remains important to develop facilities and expertise worthy of the time and resources expended in collecting seeds. Seeds of different species have different storage characteristics. Research on more than 9000 plant species has demonstrated that seeds can be grouped according to their storage behaviour into three broad categories – orthodox, recalcitrant and intermediate. Orthodox seeds are the most common and most agricultural crops produce orthodox seeds, as do plants growing in mediterranean, temperate and arid regions. Orthodox seeds undergo a drying phase as they mature on the plant and usually contain around 20–30% water when mature and ready to collect. After collection, orthodox seeds survive further drying to at least 5% water content. This enables them to be stored at freezing temperatures without harm, since there is insufficient water for lethal ice-crystals to form. Most orthodox seeds live for many years, even under less than ideal storage conditions. There are several verifiable reports of museum samples of seeds living for over 100 years, and a few reports of germinable seeds greater than 1000 years
old, based on carbon dating of archaeological samples of seeds buried in soil.1,2,3 Although there are as yet few long-term studies (greater than 10 years) providing data on longevity of seeds stored under genebank conditions, mathematical models that have been developed to predict seed longevity suggest that under ideal storage conditions, seeds of some orthodox species may live for many hundreds of years. Recalcitrant seeds are short-lived, commonly surviving for only a few days or weeks after reaching maturity. These seeds are generally produced by trees growing in tropical or temperate regions and, unlike orthodox seeds, do not undergo a drying phase during maturation, but continue to develop towards germination throughout their short life. Recalcitrant seeds are characterised by high water contents at maturity (greater than 40%) and an inability to survive drying below around 20–30% water content. As a result, recalcitrant seeds cannot be stored at freezing temperatures, and are very difficult to store for any length of time. Many large-seeded hardwoods, such as Acer pseudoplatanus (sycamore), Castanea sativa (chestnut) and numerous species of Quercus (oak) and Araucaria produce recalcitrant seeds. Relatively little is known of recalcitrant storage behaviour in Australian seeds. Intermediate seeds have properties somewhat in between those of orthodox and recalcitrant seeds. These seeds survive drying to around 10–15% water content, 53
Australian Seeds
The seedbank at Kings Park and Botanic Garden, Perth, Western Australia c. 1990. All seeds were once placed in glass jars and stored in an air-conditioned room. Photo: Luke Sweedman.
but suffer desiccation injury if dried further. Some intermediate seeds may be stored at sub-zero temperatures. Others (usually those of tropical origin) do not store well below 10°C. Seeds of Coffea and Citrus species have intermediate storage characteristics. STORAGE OF SEEDS
The primary goal of any long-term conservation collection of seeds is to maintain the initial seed viability and vigour for as long as possible. To conserve the genetic diversity contained within a carefully sampled seed accession, it is recommended that the seed viability remain at or above 85% of the original value.4 Any greater loss of viability requires re-collection of seeds from the original population, or regeneration of the stored seeds to produce new accessions for storage. Seed longevity varies greatly between species and is governed by many factors, including genotype, the initial seed quality, seed maturity at collection, postharvest handling and the storage temperature and seed water content. Genetic factors governing seed longevity and storage behaviour are characteristic of a particular species and cannot be controlled in wild collected species. Many aspects of initial seed quality are also beyond the collector’s influence, as they depend largely upon the environmental conditions experienced by the parent plant during seed maturation, and the individual species. For example, many species of Restionaceae and Cyperaceae produce few high quality, viable seed. 54
Currently, most seeds at Kings Park and Botanic Garden are stored in chest freezers held at –20°C for greater longevity, Perth, Western Australia.
However, the temperature at which seeds are stored, and the drying regime imposed prior to storage can be controlled, and it is these factors that are most crucial to successful seedbanking. For orthodox seeds, reducing the temperature and/or water content at which they are stored increases their longevity, principally by slowing metabolism and minimising deleterious ageing reactions. Generally, reducing the storage temperature by 5°C, or lowering the seed water content by 1%, doubles the storage life. Although these rules of thumb do not apply over all storage conditions, they demonstrate the relative effects of temperature and seed water content on longevity and, principally, that seed water content is the more influential factor governing seed longevity. Nevertheless, there are some interrelationships between temperature and seed water content, and reducing both will provide greater longevity than reducing one alone. Current international guidelines recommend storing orthodox seeds at −18°C and 3–7% water content.5
Chapter 7 – Seed storage and testing
The main vault at the Millennium Seed Bank Project, Wakehurst Place, UK. Seeds are stored in glass jars inside the vault, which is held at −18°C. Photo: Luke Sweedman.
SEED DRYING PRIOR TO STORAGE
The fact that a relatively small change in seed water content can have such a large impact on longevity emphasises the importance of correctly drying seeds before storage, particularly for long-term conservation collections. Even if seeds cannot be stored at a low temperature (in the absence of power, for instance), reducing the water content will be of great benefit to longevity. Drying seeds provides additional benefits by reducing the risks of attack by micro-organisms and protecting seeds from freeze injury (caused by ice-crystal formation) if they are stored at sub-zero temperatures. Seed drying is based on the principle that most seeds readily adsorb water from, or lose water to, the surrounding atmosphere until they reach an equilibrium. Therefore, seed water content may be manipulated by placing the seeds in sealed containers (or rooms) of controlled relative humidity. Freshly collected seeds are often dried in two stages. They should be initially dried as soon as possible after collection, before cleaning and sorting, ideally by placing the collected material in porous bags or laying them out on trays and storing them in a cool room at low humidity for a few weeks. Note, however, that collections containing a high proportion of immature seeds should be dried slowly at first to encourage ripening, as seeds must be mature before they are able to tolerate rapid drying. Ambient humidity is sometimes suitable for initial drying of freshly collected seeds, although in tropical areas or during the wet season this may not be the case. It
is important to remember that seeds should always be dried at a cool temperature and low relative humidity, rather than by exposure to high temperatures. Following cleaning, seeds should then undergo a second, tightly controlled drying process to reduce the water content to an optimum level for storage. Both temperature and relative humidity affect seed water content, and the optimum combination for drying is still a matter of considerable research. However, for routine storage, advanced seedbanks such as the Millennium Seed Bank Project (Wakehurst Place, UK) dry seeds at 18°C and 15% relative humidity. Similarly, the Botanic Gardens of Adelaide and the Western Australian Seed Technology Centre maintain drying rooms at 15°C and 15% relative humidity. Drying seeds within this range of conditions (15–20°C and 10–15% RH) is currently considered best practice for orthodox seeds.6 For smaller operators without access to controlled drying facilities, alternative methods of drying are available. One easily applied and inexpensive method of drying is to place the seeds inside a sealed vessel containing silica gel. A ratio of 3 kg of silica gel per 1 kg of seeds should be used to avoid risks of over-drying, as well as the need to regenerate the silica gel too frequently. (Freshly regenerated silica gel provides an atmosphere of around 5% relative humidity at room temperature.) Silica gel is regenerated by placing in an oven at 130°C for several hours, and this should be done at the first sign of a colour change (usually from a dark blue to a lighter blue or pink). Greater control over seed water content can be
A dehumidifying cabinet used to reduce seed water content prior to freezing.The plastic boxes contain silica gel. Cordoba, Spain. Photo: Luke Sweedman.
55
Australian Seeds
Hygrometers are a useful, non-destructive measure of seed water status.The equilibrium relative humidity of seeds placed in the chamber is determined.
gained by equilibrating seeds over saturated salt solutions such as lithium chloride, which will provide an atmosphere of around 11–13% relative humidity at room temperature. Virtually any relative humidity can be achieved using different salt solutions, although this method requires greater technical knowledge and is more expensive than silica gel. Once seeds have been dried, they need to be placed in air-tight containers to prevent re-absorption of water from a humid ambient environment. Commonly used containers include screw-top glass jars or vials, metal cans and laminated heat-sealable foil bags. The choice of container depends largely on the resources and space available, but it is vital that the container seal is airtight. A good heat seal is essential for foil bags to remain airtight and it is recommended that a seal at least 10 mm wide be applied. Laminated foil bags are the most space-efficient containers, and probably the most practical for storing in a domestic freezer. Glass jars with a rubber seal and clamped lid also produce a good seal. Although they require much more space, glass jars have the advantage of allowing visual inspection of how much seed is available. Small packets of silica gel indicator may also be placed in glass jars, enabling confirmation of an airtight seal. CALCULATION OF SEED WATER CONTENT
Seed water content should be tested following the final drying, just before storage, and then again at occasional intervals to ensure the storage containers have remained airtight. Seed water content can be calculated easily by 56
weight. The standard method requires fresh seed samples to be weighed, placed in an oven at 103°C for 17 hours (low temperature method for oily seeds) or 130°C for three hours (high temperature method for non-oily seeds), and then weighed again.7 Seed water content can then be calculated as a percentage: Seed water fresh weight of seed – dry weight of seed × 100 content = dry weight of seed
Note that seeds of different species will have different water contents when dried under the same conditions because of variations in oil content. Measuring seed water content gravimetrically is an accurate and reliable method; however, the seeds are killed in the process. Alternative, non-destructive methods of determining seed water content are now available, and the use of these techniques is becoming more common. Electronic hygrometers measure the water status of seeds by measuring equilibrium relative humidity following the placement of seeds in a small chamber attached to the instrument. Hygrometers provide a rapid determination of whether seeds have reached an equilibrium with the drying environment. (Seeds dried in a room held at 15% relative humidity should display an equilibrium relative humidity of 15%.) STORAGE TEMPERATURE
Correctly dried and packaged seeds should be transferred immediately into storage. The choice of temperature
Chapter 7 – Seed storage and testing
depends largely on the purpose of the collection and the available resources. For some operations, this may be storage at ambient temperatures or in an air-conditioned room. These conditions may be ample for seeds that are to be stored only for short periods, and indeed may be beneficial with regard to overcoming physiological dormancy in some seeds by allowing after-ripening to occur. However, if seeds are to be stored for more than a couple of years, a lower temperature is preferable. Household refrigerators are capable of maintaining a constant temperature of around 0–5°C and are an inexpensive method of storing seeds. For commercial operations or landcare and community groups storing seeds for up to five years, refrigerated storage is ideal. For longterm conservation collections (greater than 5–10 years storage), commercial freezers that operate at temperatures of around −18°C may be used to prolong viability. When storing seeds at sub-zero temperatures, it is important to make sure that correct drying procedures have been followed, as a combination of sub-zero temperatures and high seed water contents may result in lethal ice-crystals forming within the seeds. Some seedbanks and laboratories store seeds in liquid nitrogen (cryostorage). The temperature of liquid nitrogen is −196°C and seeds stored at this temperature may live for many hundreds (or possibly thousands) of years. Such a secure method of storage is invaluable for conservation of rare and endangered species as there is often very little seed available for collection, and reintroduction of a species may require long-term planning. Cryostorage has traditionally been used for storage of economically important species. However, it is increasingly being adapted to wild species of conservation value.
The benefits of cryostorage must be weighed against the high set-up costs and reduced storage capacity of liquid nitrogen dewars, as well as the greater technical expertise required. SEED TESTING
The main considerations when determining the quality of a new batch of seeds are purity, viability and germination. The purity of the seed batch relates to the proportion of seed to non-seed material. Many seed batches contain non-seed material such as chaff, seed decoys and floral parts. Careful cleaning should ensure a high purity, which is important as it aids in uniform seed drying and reduces the weight and volume of a seedlot and the space required for storage. A viability test provides an estimate of whether a seed is alive or dead, and therefore the proportion of seeds which has the potential to germinate. A germination test subsequently determines the proportion of viable seeds that is able to germinate. A reliable germination test is the most accurate method of assessing the health of a seed accession. VIABILITY TESTING
A viable seed is one which is alive, and the term refers to both readily germinable seeds, and seeds that are dormant. Viability is often taken to be synonymous with germination, but they are two separate concepts. A seed may be viable, but this does not imply that it is germinable; the seed may be dormant and will remain so until it is exposed to dormancy-breaking conditions and favourable germination conditions arise. Many methods are available to determine seed viability. All of them require a sample of seeds to be taken from
A simple viability test is the cut test.This involves removing the seedcoat and visually inspecting the seed for the presence of healthy embryonic tissues.These should appear plump, turgid and generally a healthy white or pale yellow colour. Cracking of the endocarp of Emblingia calceoliflora seeds (left) reveals the seed within (centre), and careful removal of the seedcoat allows inspection of the turgid, white endosperm and healthy coiled embryo (right).
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Australian Seeds
A seed of Dioscorea hastifolia with extracted embryo (left), and a close-up of the healthy embryo following staining with tetrazolium chloride (right).
An extracted embryo of Opercularia vaginata following tetrazolium chloride staining.The variable staining pattern of this embryo suggests it may not be viable.
each seed batch to enable estimation of the proportion of viable seeds in the whole population. The sample of seed removed for viability testing should be divided into replicates of equal number and the results averaged. It is important to perform the test on each batch of seed collected from different sites or in different years, as environmental conditions experienced by the parent plant during seed development play a major part in seed viability. One method of viability testing is embryo excision. This involves carefully removing the embryo of the seed from the surrounding tissues and culturing it in vitro in water or on growth media. If the embryo grows, the seed it came from is deemed viable. This method is particularly 58
useful for difficult to germinate, dormant seeds. However, embryo excision is labour intensive and requires skilled staff and usually some experimentation to determine a suitable composition of growth medium. Embryo excision is therefore not practical for non-laboratorybased operators. A more simple viability test is the cut test. This involves removing the seedcoat and visually inspecting the seed for the presence of healthy embryonic tissues. These should appear plump, turgid and generally a healthy white or pale yellow colour. Seeds containing dry, shrivelled and/or brown tissues are usually non-viable (as, of course, are empty seeds). Seeds of many Australian species are very small, and visual inspection of the embryo may require the aid of a hand lens or dissecting microscope. An even quicker (but less reliable) viability test is the float test. This involves placing a sample of seeds in a jar of water and recording the number which float versus the number which sink. Viable seeds sink to the bottom, while non-viable seeds float. However, this test is not infallible as some species produce seed which all float (or all sink) regardless of the viability. It is advisable to calibrate the float test by first doing a cut test and comparing the results to the float test. Other methods of viability testing that may be used are based on staining the embryonic tissues of seeds to test for the presence (or absence) of biochemical activity. Tetrazolium chloride (TTC), Fluorescein diacetate (FDA) and Evans Blue are examples of stains that may be used to estimate seed viability. Tetrazolium chloride is probably
Chapter 7 – Seed storage and testing
the most commonly used stain. This chemical reacts with dehydrogenase enzymes that are involved in respiration. A positive test, which results in the tetrazolium solution changing from colourless to pink or red, indicates respiration and, therefore, a live seed. To use tetrazolium, seeds are usually first imbibed in water and the seedcoat nicked or removed, or the seed cut in half to expose the embryonic tissue. The seeds are then placed in a 1% solution of tetrazolium and incubated for several hours at 20–30°C. Seed viability is interpreted according to the staining pattern of the embryo and the intensity of the colour. With all stains, scoring viability is often somewhat subjective. The embryonic tissues may be partly alive and partly dead, meaning different areas of the embryo may colour to different degrees. Interpreting the staining patterns can be difficult and may provide erroneous results without calibrating the staining pattern using other methods. However, the advantages of using stains include the speed of the tests and their usefulness in estimating the viability of dormant seeds that have unknown germination requirements. GERMINATION TESTING
Regular germination testing is the only sure method of determining whether the selected storage conditions are maintaining seed quality over time. International genebank standards recommend that the first germination testing be conducted after 10 years’ storage for seeds stored under ideal conditions or after five years for seeds with poor initial quality or longevity.8 However,
for seeds with unknown storage behaviour (i.e. the majority of Australian species), it is advisable to take a more cautious approach and test germination more frequently, perhaps following one, two and five years’ storage. If no reduction in germination is noted during this time, then seeds may be tested less frequently, perhaps again after 10 years’ storage. When deciding on the frequency of testing, staff and resource availability needs to be considered, as does the number of seeds initially collected. Similar to the viability test, a germination test requires a sample of seeds from each batch to be removed to allow a calculation of the percentage germination. Ideally, the total sample size should be at least 50 to 100 seeds, and it is recommended that the initial germination test be performed using 200 seeds.9 In many cases wild seeds are in short supply and it is impossible to use such a large number of seeds for testing. However, wherever possible, replicate tests should be made, and each batch of seed from a different location or collected at a different time needs to be tested. In order to germinate, non-dormant seeds require water, oxygen and incubation at the correct temperature. Some species also have special light requirements. A common technique for germinating seeds in the laboratory is to incubate them in Petri dishes at the required temperature. Generally, an equal number of seeds per replicate is placed on filter paper, germination test paper, sand or vermiculite in a Petri dish and moistened with water. Alternatively, water agar (at around 0.7–1.0% weight/volume) can be used as a germination medium.
Two different methods of seed germination testing. Seeds of Regelia ciliata incubated in a Petri dish on 0.7% water agar (left), and seeds of Corymbia calophylla sown in nursery soil and placed in a glasshouse (right). 59
Australian Seeds
Seeds of many Australian species require sterilisation prior to incubation in Petri dishes to reduce the growth of endogenous fungi and bacteria which may occasionally reduce germination. Seeds may be sterilised in a weak solution (1–2%) of sodium hypochlorite (bleach) for 10 to 15 minutes (sometimes up to 45–60 minutes) and then washed in sterile water. The need for sterilisation can be negated if a commercial fungicide is added. It is important to note that the sterilisation procedure itself may sometimes damage sensitive seeds. Thus, care is needed not to expose seeds for lengthy periods or to high concentrations of the sterilant. Temperature is critical to successful germination and if it is too cold or too hot a poor germination result may give the false impression of an aged seed batch and an inappropriate storage regime. Thus, seeds removed from storage for germination testing must always be incubated at the same temperature. In the absence of detailed information, the optimum germination temperature often can be estimated from a knowledge of the parent plant’s habitat. An incubation temperature corresponding to the average air temperature during the wet season (or in the months at which seeds of the species are known to germinate) is usually suitable. For example, species from the southwest of Western Australia usually have optimal incubation temperatures of between 15–20°C, while species growing further north in semi-arid regions germinate best at temperatures between 25–35°C. If no temperature control is available, it is preferable to test seeds at the time of year at which they naturally germinate in the wild. IMBIBITION INJURY
An additional consideration when removing seeds from storage for germination testing is the possibility of imbibition injury. If seeds have been stored at very low water contents, the sudden and rapid influx of water may damage cells and kill the seeds. When germinating seeds which have been stored for many years, or at very low water contents (less than around 5%) it may be necessary
60
to place them above (not directly in) water in a sealed container for 24 hours before placing them in a germination medium. This provides an atmosphere of 100% relative humidity, allows the seeds to take up water gradually and prevents imbibition damage. SCORING RESULTS
Records such as the time to initial and maximum germination, the number of seeds germinated and the rate of seedling growth provide information on the health and vigour of a seed batch, which can then be related to the storage conditions. Ideally, seeds should be checked and scored every two to three days for germination to allow an accurate calculation of the rate of germination. An additional consideration when determining the percentage germination is the viability of the seed batch. It is more accurate to express germination results based on the number of viable seeds (i.e. the number of seeds capable of germinating, not the total number of seeds tested). If a seed batch has only 50% viability, 100% of the sown seeds should not be expected to germinate. Germination results can be corrected for viability using the concept of Viability Adjusted Germination (VAG). This is calculated using the following formula: VAG =
% germination × 100 % viability
For example, if a germination test records 60% germination, and the seed batch was assessed to have 75% viability, then the VAG is 80%. This concept is useful not only for low-viability seed batches, but when dealing with seeds with unknown dormancy mechanisms. If a new dormancy-breaking treatment is applied to a low-viability seed batch, without taking into account the small proportion of those seeds capable of germinating, it may be erroneously concluded that a low percentage germination means the treatment is ineffective when, in fact, it resulted in all of the viable seeds germinating.
CHAPTER 8
Seedbanks and the conservation of threatened species Anne Cochrane and Leonie Monks
Loss of biodiversity is one of the major environmental threats facing the world today. Natural resource management strategies that aim to integrate in situ (on-site) and ex situ (off-site) approaches to conservation merit considerable attention. Seedbanking for conservation purposes offers an opportunity to reduce the impact of species extinction and loss of biodiversity. It ensures that even if species are lost in the wild, plants will be available for future conservation actions and utilisation. It is one of many complementary conservation management strategies that are available to counter the impact of biodiversity loss. Seedbanking is considered the safest, most inexpensive and most convenient method of ex situ conservation for flowering plants. Seedbanking has been used for many decades to conserve seed of agricultural species, with the primary objective to conserve plant genetic resources for use in plant improvement programs. Wild species diversity has largely been ignored, with the establishment of native seedbanks for biodiversity conservation a relatively recent occurrence, particularly in Australia. The extension of the operation of ex situ facilities to involvement in recovery projects, such as the reintroduction of threatened species and the restoration of degraded plant communities, is an even more recent phenomenon, and one that has received international sanction through the Convention on Biological Diversity (CBD).
In some cases, ex situ conservation represents the only option available if the remaining natural populations are to be conserved in the face of destruction of their habitat. Actions to conserve individual species contribute in a fundamental way to broader conservation objectives, even if the species themselves are not highly threatened. Seedbanking cannot directly protect biological diversity of ecosystems, but it can ensure the protection of genetic diversity. Off-site flora conservation can:
• •
provide material for species and ecosystem recovery;
•
maximise the value of the material for sustainable use in research and recovery, through investigations into seed germination and storage behaviour;
• •
contribute to education and public awareness; and
provide a readily accessible and cost-effective source of material for research;
provide critical biophysical information for writing and implementing management and recovery actions.
In the first instance, seedbanks should establish priorities for collection and storage, with the most urgent candidates for ex situ conservation being plant species under severe threat in the wild. Priorities for collection should include:
61
Australian Seeds
•
Species with low plant numbers, few populations, or limited geographic range;
• •
endemics; those highly threatened by human and other influences (for example disease, salinity, exotic weed invasion and grazing);
•
those experiencing rapid decline in status or health; and
•
those thought to be genetically or taxonomically different from a more common species.
The feasibility of taking a species into cultivation and its potential for recovery may also influence the collection priorities. Conservation collections are only as good as the diversity they contain and correct sampling is one of the fundamental pillars of good conservation policy. Collecting quality seed stock on a provenance basis, prior to a reduction in genetic diversity and/or inbreeding depression, should ensure that material for long-term storage and research contains maximum genetic diversity. Genetic diversity is the basis for an organism to adapt to its existing environment and for its potential to adapt to future environmental changes. Thus, loss of genetic variability can diminish the adaptive ability of a species. Understanding genetic differences (i.e. the structure of genetic variation within and between populations) permits more accurate and successful collection strategies for material to be used in reintroduction projects and careful genetic planning to maintain the fitness of the population. This can be achieved by directing collection activities over a number of known populations of the species and by collecting from a wide range of individual plants covering ecotypic and genotypic variation within each population. Ensuring that material collected from different populations and/or individuals is not mixed is vitally important in maintaining genetic integrity in a recovery programme, for determining the genetic blueprint of a species, and for assessing possible differences in tolerance to threats and to varying germination conditions. This type of collection will be more useful for research and recovery than a sample of seed collected without regard to genetic variation. In contrast, collecting for horticultural or display purposes may warrant selecting material
62
for a desirable trait, such as colour, shape or form, rather than for a representation of the genetic diversity of the species. UTILISATION OF SEED
Ex situ conservation provides protective custody of threatened plant species and is justifiable only as part of an overall conservation strategy that ensures species survival in the wild. An ex situ strategy for biodiversity conservation of threatened plant species should always be complementary to in situ conservation. An ex situ collection allows access to material for research at any time of the year without impacting further on wild populations. Ex situ material can be used for genetic studies, seed research, and disease and salinity susceptibility and tolerance investigations. Material is available for a range of recovery actions, particularly reintroduction of single species and restoration of threatened ecological communities should the need arise. In addition, material is also on hand for education and display. Research
Ex situ conservation programs can make important contributions to understanding the reproductive biology of threatened species. Research into the germination requirements of native plants can contribute to the successful recovery and restoration of species and communities. Understanding seed germination characteristics also provides benefits to the horticultural industry. Seedbanks can provide material to identify susceptibility of species to introduced pathogens, and material from ex situ collections may be used in the future to identify salinity and waterlogging tolerance in threatened species. Material from ex situ collections can be made available for research into conservation genetics, providing the basis for sound sampling strategies to be formulated for critically threatened native species. Insights gained from scientific studies can help set conservation priorities, provide help for on-ground management and conservation of the species, and assist in the development of management plans that include species reintroductions. Species recovery
An essential part of the recovery process involves the scientific management of ex situ collections and their reintroduction into managed environments. Recovery
Chapter 8 – Seedbanks and the conservation of threatened species
plans often recommend ex situ conservation precede a reintroduction programme, thereby allowing sufficient time for important biological characteristics of the species to be assessed. Reintroduction, or translocation, is the deliberate transfer of material from one place to another for the purpose of conservation. Reintroduction of plant material to the wild is one of the management strategies ensuring that extinctions of threatened flora are minimised, and it provides support for survival of existing populations in the natural environment. Species reintroduction programs aim to retain the genetic diversity expressed by that species. The selection of plant material to be used in such recovery projects is critical to the long-term goal of creating self-sustaining populations. Seed collection should therefore be linked to a recovery plan to allow for the selection of the most appropriate method of collection and storage. Seeds or vegetative material can be used in recovery programs, and the type of material chosen will reflect the most successful method of propagation for the species concerned. Seeds are generally considered the cheapest and easiest form of propagules to store. In addition, the likelihood of obtaining broader genetic variation in material produced through sexual reproduction is higher than expected for vegetative material. This variability is essential if the population is to be able to respond adaptively to environmental changes. Sampling from a broad range of plants means that the collection has the potential to represent the species. If individual propagule survival during storage or cultivation diminishes, then the ability of the stored material to represent the genetic diversity of the sampled population is compromised. Education and display
Educating the public about threatened plants helps increase the likelihood that additional populations will be discovered and reduces the risk that rare plants will be accidentally damaged or destroyed. A relatively simple way of increasing public awareness about threatened plant species is the display of such species in rare flora gardens and at wildflower shows. Seedlings from viability tests undertaken as part of the long-term ex situ storage protocol are often used for this purpose.
CASE STUDY: GREVILLEA CALLIANTHA (PROTEACEAE)
Foote’s grevillea (Grevillea calliantha) was first discovered in 1981, near Cataby, approximately 150 km north of Perth, Western Australia. The species forms a spectacular, compact shrub that grows to around one metre in height and produces masses of red and black flowers in spring. The species name refers to these spectacular displays of flower – calliantha is derived from the Greek meaning ‘beautiful flower’. The pods ripen in November and contain two seeds that are surrounded by a fatty appendage attractive to ants. These seeds are dormant on dispersal. Grevillea calliantha was declared as Rare Flora in 1989. In September 1995 it was listed as Critically Endangered as only six populations, totalling 137 plants, were known. Four of the populations occur on narrow road verges where they are vulnerable to being damaged or destroyed through road maintenance activities. The remaining two populations occur on private property and shire reserve, where grazing by stock and native animals and inappropriate fire regimes are of concern. An Interim Recovery Plan that made recommendations on the actions needed to recover the species was prepared. One of the actions recommended was collection and storage of seeds in a long-term germplasm storage facility. In November 1995 seeds of this species were collected for ex situ conservation. Three visits were necessary to ensure seed was collected at peak maturity. Seeds were collected from a wide range of plants throughout four of the six populations, to ensure capture of a broad genetic base. A small sample of the seeds collected were tested for germinability prior to long-term storage. Seed moisture content was reduced to equilibrium under low temperature and low moisture conditions (15°C and 15% relative humidity) prior to storage at −20°C in laminated aluminium foil bags. In addition to seed collection, the Interim Recovery Plan also recommended initiating the translocation process. In November 1997 one hundred seeds were removed from storage for germination. The resulting 79 seedlings were sent to an accredited nursery for cultivation. In addition to these seedlings specifically germinated for the translocation programme, any germinants of G. calliantha that resulted from routine germination testing as part of the seed storage process were also included in the translocation process. Under an approved translocation proposal these seedlings (totalling 106 individuals) were planted at a new site in a reserve in August 1998.
63
Australian Seeds
The spectacular inflorescences of Grevillea calliantha are produced en masse in spring.
Despite Grevillea calliantha producing 15–30 flowers per inflorescence, the flower-to-fruit ratio is very low. Immature fruits are viscid and often striped red.
After four years, 45 plants (42%) survived at the translocation site. All have flowered and set seed. Fresh seeds were again collected in November 1998 for augmenting the translocation site. Of the 245 seeds collected, a total of 115 seedlings resulted. After three years, 76% of these seedlings survived at the translocation site. A further 220 plants derived from cutting material were planted at the site over the next two years. As a consequence of these four successive years of planting, there are now well over 300 plants at the translocation site. Many of these have flowered and set seed. Although naturally recruited seedlings have not been observed to date, it is still early days. Seed collection and storage, followed by translocation to a new site, has resulted in a positive outlook for the long-term survival of this species in the wild. CASE STUDY: DAVIESIA BURSARIOIDES (FABACEAE)
Three Springs Daviesia (Daviesia bursarioides) is a straggling shrub that grows to 2 m in height and produces delicate yellow and maroon, pea-shaped flowers from July to September. The fruit is a pod that dehisces seeds explosively on ripening in November. The small hardcoated seeds are dormant in the absence of heat shock or seedcoat scarification, and hence the species is able to form a persistent soil seed reserve. The species was first collected in 1932 near the small country town of Three Springs, 300 km north of Perth, but by 1978 only one surviving population, with three adult plants, was 64
Translocated plants of Grevillea calliantha are protected from herbivore grazing by strong wire cages. Photo: David Coates.
known. Consequently the species was listed as Declared Rare Flora in 1987. Since 1990, five new populations within a 30 km geographic radius of the original plants have been found, bringing the total number of populations to six. However, there were only 123 plants in total within these six populations. Four of the populations occur on narrow road verges where they are vulnerable to damage or destruction during road maintenance. As a result the species was ranked as Critically Endangered in September 1995. An Interim Recovery Plan was written to identify the actions needed to recover the species. The Plan recommended seed collection and storage as well as restocking one of the known populations or translocation to another site. Between 1995 and 1997, seeds were collected from four of the known populations from at least 30 individuals. The majority of seeds were dried to equilibrium at 15°C and 15% relative humidity and sealed in laminated aluminium foil bags (seed from individual plants was kept separate) and stored at −20°C. A small sample of seed from each collection was germinated after pre-treatment but the germination percentage was generally low. After one year in storage, 374 seeds from a 1996 collection were removed. These seeds were pre-treated in the same manner as seeds germinated prior to storage. Germination was slightly higher (55%) than that recorded for fresh seed (48%). Germinants were sent to a nursery and six months later a total of 192 seedlings were
Chapter 8 – Seedbanks and the conservation of threatened species
Striking yellow and maroon, pea-shaped flowers of Daviesia bursarioides.
These immature fruits of Daviesia bursarioides will open explosively when ripe.
available for planting. Augmentation planting took place in September 1999. After four years, 39 of these seedlings (20%) had survived at the translocation site. Almost all of these plants (31) have flowered and set seed. Subsequent seed collections were made in November 1998 with the aim of introducing more seedlings to the translocation site. From this collection 201 seeds were used for germination testing and propagation. After six months, 144 seedlings were available for translocation. These were planted in August 1999. After three dry years and grazing pressure from kangaroos only 19 of these plants survived. A further 450 seeds were removed from storage, germinated and sent to the nursery. The resulting 262 seedlings were planted at the translocation site in July 2000. Again the dry years resulted in just 10 plants surviving by 2002. The three-year translocation programme resulted in 68 extra plants being established at the augmentation site. Before translocation just 12 individuals occurred at this site. Translocation has therefore increased the population size five-fold. Many of the translocated plants have flowered and set seed. It is probable that natural recruitment will not occur in the absence of disturbance, owing to the restriction of the hard seedcoat that prevents germination. Despite lack of recruitment, it is likely that a soil seed reserve is being created at the translocation site that will be viable for many years. In the event of a disturbance such as fire, this species should be able to regenerate from this seed reserve. Whilst the species is still critically
Volunteers augmenting a natural population of Daviesia bursarioides.
endangered, seed collection, long-term seed storage and translocation will help ensure species survival in the wild in the long term. CASE STUDY: LAMBERTIA ORBIFOLIA SUBSP. ORBIFOLIA (PROTEACEAE)
Lambertia orbifolia subsp. orbifolia is an attractive upright shrub or small tree (up to 4 m tall) that grows near Narrikup, 50 km north of Albany on the south coast of Western Australia. The name of the species refers to the rounded or orb-shaped leaves. The common name, Round-Leaf Honeysuckle, refers to the honeysuckle-like orange-red flowers that occur in clusters of four to six from May to July and then again from December to January. There is no defined fruiting period in this species and the weakly serotinous pods can be collected throughout the year. Each pod contains two flat, round to triangular, black seeds that are non-dormant on dispersal. Plants are killed by fire, regenerate readily from seed and are highly susceptible to root-rot disease caused by Phytophthora cinnamomi. In 1999, two populations occurred at Narrikup that consisted of just 169 plants. The populations occurred on degraded road verges and were in relatively poor condition, being affected by disease (aerial canker and dieback) and exotic weed invasion. As a consequence this subspecies was listed as critically endangered in September 1999. An Interim Recovery Plan was written for the subspecies, which recommended further survey, 65
Australian Seeds
The honeysuckle-like orange-red flowers of Lambertia orbifolia subsp. orbifolia are attractive to birds who are major pollinators of this subspecies. Photo: Kate Brown.
Fruits of Lambertia orbifolia subsp. orbifolia are clasped within the orbicular-shaped leaves of the plant. On ripening, seeds are released and germinate readily.
ex situ germplasm storage and translocation. Surveys undertaken in 1999 and 2000 located one new population, which substantially increased the number of known individuals to 944. A small amount of seeds was collected over a number of years from more than 50 plants. These seeds were collected between 1992 and 1996 for ex situ storage. Viability of seeds was high (up to 100%) with only one early collection showing a decrease in viability in storage over five years. In 1998 seedlings of L. orbifolia subsp. orbifolia were translocated to a conservation reserve less than 4 km from the known Narrikup populations. Stored seeds from both populations were germinated in 1997–98. Low genetic diversity between the two original populations enabled mixing of the populations, thereby guaranteeing a greater number of source plants for the translocated
population. Seedlings were transferred to the nursery for cultivation and in winter 1998, 216 six-month-old seedlings were planted at the translocation site. In 1999 a further 330 plants were translocated into the site. These were a mixture of cutting and seedling derived plants. After four years, 163 plants (75%) from the 1998 planting survived. All have flowered and produced viable seeds and second generation seedlings recruited for the first time in 2002. After three years, 246 (74%) of the 1999 planting survived. Another 69 seedlings were translocated into the same site in 2000. Heavy grazing from kangaroos resulted in just six (9%) of these surviving. To date there are 490 plants at the translocation site making it the second largest population of this subspecies. Natural seedling recruitment observed in 2002 should ensure a high probability of survival for this subspecies in the wild in the long term.
66
CHAPTER 9
Australian seeds: a photographic guide Luke Sweedman
This chapter contains photographs of seeds of more than 1200 species that are held in the seedbank at the Seed Technology Centre, Kings Park and Botanic Garden, Perth, Western Australia. Rather than showing every species in a genus we have attempted to show the great range of diversity of seeds found within different genera. In many cases there is considerable variety in either shape or colour between species, and the seeds can be used as a significant tool for diagnostic identification.
The seeds of some species such as Eremophila are stored while still in the fruit.
Most of the species photographed are referenced to the herbarium specimens and a list of collection numbers is given in Appendix 2 of this book. This provides a direct link from the photograph to the naming and collection record for that species. The seeds are measured as accurately as possible and the size shown beside the photographs is generally the length. Seeds are not uniform in size and therefore this is a guide only. The very small seeds, those below about 1 mm in size, are not easily distinguished and groups such as Melaleuca are particularly obscure in shape and form. Those seeds too difficult to view with the naked eye or with a field hand lens have therefore been photographed under a microscope. Although the seeds were originally photographed for their affinity with the genus they belong to, they have immense natural beauty that shines as you look through the photographs. They are interesting enough in themselves to enjoy the shapes, forms and textures. Their range of colours and their sheer variety is startling. In some cases, the photographs are of fruits rather than seeds, for example Leucopogon, Eremophila and Scaevola. For these species the seeds are stored while still in the fruits and cannot be removed easily.
67
Australian Seeds
Abildgaardia schoenoides
Abutilon cunninghamii
3 mm CYPERACEAE
Abrus precatorius
7 mm FABACEAE
Abutilon cryptopetalum
2 mm MALVACEAE
2 mm MALVACEAE
Acacia acuminata
5 mm FABACEAE
Acacia aestivalis
10 mm FABACEAE
Acacia alata
4 mm FABACEAE
Acacia amblyophylla
8 mm FABACEAE
Acacia anaticeps
13 mm FABACEAE
Acacia aneura
6 mm FABACEAE
Acacia anfractuosa
4 mm FABACEAE
Acacia aphylla
5 mm FABACEAE
68
Australian Seeds
Acacia argyraea
5 mm FABACEAE
Acacia arida
4 mm FABACEAE
Acacia armata
4 mm FABACEAE
Acacia atkinsiana
5 mm FABACEAE
Acacia bivenosa
7 mm FABACEAE
Acacia burkittii
4 mm FABACEAE
Acacia celastrifolia
4 mm FABACEAE
Acacia citrinoviridis
8 mm FABACEAE
Acacia cochlearis
3 mm FABACEAE
Acacia colei var. colei
4 mm FABACEAE
Acacia coolgardiensis
3 mm FABACEAE
Acacia coriacea
10 mm FABACEAE 69
Australian Seeds
Acacia cowleana
4 mm FABACEAE
Acacia cyclops seed variation 1
7 mm FABACEAE
Acacia cyclops seed variation 2
7 mm FABACEAE
Acacia demissa
9 mm FABACEAE
Acacia denticulosa
4 mm FABACEAE
Acacia drepanocarpa
7 mm FABACEAE
Acacia drummondii subsp. drummondii
4 mm FABACEAE
Acacia dunnii
12 mm FABACEAE
Acacia filifolia
3 mm FABACEAE
Acacia galeata
6 mm FABACEAE
Acacia gilesiana
7 mm FABACEAE
Acacia gonoclada
4 mm FABACEAE
70
Australian Seeds
Acacia grasbyi
7 mm FABACEAE
Acacia harveyi
5 mm FABACEAE
Acacia hemignosta
6 mm FABACEAE
Acacia hemiteles
3 mm FABACEAE
Acacia heteroneura var. prolixa
4 mm FABACEAE
Acacia hilliana
5 mm FABACEAE
Acacia holosericea
4 mm FABACEAE
Acacia horridula
5 mm FABACEAE
Acacia inaequilatera
5 mm FABACEAE
Acacia jibberdingensis
5 mm FABACEAE
Acacia lasiocalyx
8 mm FABACEAE
Acacia longispinea
3 mm FABACEAE 71
Australian Seeds
Acacia lysiphloia
3 mm FABACEAE
Acacia merrallii
4 mm FABACEAE
Acacia merrickiae
5 mm FABACEAE
Acacia myrtifolia
4 mm FABACEAE
Acacia neurophylla
3 mm FABACEAE
Acacia oldfieldii
3.5 mm FABACEAE
Acacia pharangites
3 mm FABACEAE
Acacia plectocarpa
4 mm FABACEAE
Acacia prainii
6 mm FABACEAE
Acacia pruinocarpa
6 mm FABACEAE
Acacia pulchella
3 mm FABACEAE
Acacia pygmaea
4 mm FABACEAE
72
Australian Seeds
Acacia resinimarginea
3 mm FABACEAE
Acacia retivenea
5 mm FABACEAE
Acacia rhodophloia
7 mm FABACEAE
Acacia rossei
5 mm FABACEAE
Acacia rostellifera
5 mm FABACEAE
Acacia saligna
4 mm FABACEAE
Acacia sclerosperma
9 mm FABACEAE
Acacia semicircinalis
5 mm FABACEAE
Acacia sessilispica
2 mm FABACEAE
Acacia sibina
4 mm FABACEAE
Acacia splendens
7 mm FABACEAE
Acacia subflexuosa
2 mm FABACEAE 73
Australian Seeds
Acacia sulcata var. planoconvexa 3 mm FABACEAE
Acacia tetragonophylla
4 mm FABACEAE
Acacia translucens
7 mm FABACEAE
Acacia tumida
5 mm FABACEAE
Acacia validinervia
5 mm FABACEAE
Acacia vassalii
5 mm FABACEAE
Acacia victoriae
4 mm FABACEAE
Acacia wiseana
7 mm FABACEAE
Acacia xiphophylla
8 mm FABACEAE
Acanthocarpus preissii
74
5 mm LAXMANNIACEAE
Acidonia microcarpa
10 mm PROTEACEAE
Actinostrobus acuminatus
10 mm CUPRESSACEAE
Australian Seeds
Actinostrobus pyramidalis
Adriana quadripartita
Albizia lebbeck
Allocasuarina acutivalvis
5 mm CUPRESSACEAE
8 mm EUPHORBIACEAE
8 mm FABACEAE
13 mm CASUARINACEAE
Actinotus leucocephalus
Agonis baxteri
Alectryon diversifolius
5 mm APIACEAE
2 mm MYRTACEAE
7 mm SAPINDACEAE
Allocasuarina decaisneana 15 mm CASUARINACEAE
Adansonia gregorii
Agonis flexuosa
Alectryon oleifolius
Allocasuarina fibrosa
13 mm BOMBACACEAE
0.75 mm MYRTACEAE
6 mm SAPINDACEAE
6 mm CASUARINACEAE 75
Australian Seeds
Allocasuarina fraseriana
Alphitonia incana
Amaranthus mitchellii
Andersonia involucrata
76
8 mm CASUARINACEAE
6 mm RHAMNACEAE
1 mm AMARANTHACEAE
1 mm ERICACEAE
Allocasuarina microstachya 5 mm CASUARINACEAE
Allocasuarina pinaster
Aluta maisonneuvei
2 mm MYRTACEAE
Alyogyne hakeifolia
4 mm MALVACEAE
3 mm POACEAE
Amyema fitzgeraldii
7 mm LORANTHACEAE
Amphipogon strictus
Angophora costata
4 mm MYRTACEAE
Anigozanthos bicolor
10 mm CASUARINACEAE
2 mm HAEMODORACEAE
Australian Seeds
Anigozanthos flavidus
2 mm HAEMODORACEAE
Anigozanthos gabrielae 1.5 mm HAEMODORACEAE
Anigozanthos humilis
1.5 mm HAEMODORACEAE
Anigozanthos manglesii 2 mm HAEMODORACEAE
Anigozanthos preissii
Anigozanthos viridis
1.5 mm HAEMODORACEAE
Anisomeles malabarica
Anthocercis genistoides
2 mm LAMIACEAE
Aphanopetalum clematideum 3 mm CUNONIACEAE
2.5 mm HAEMODORACEAE
2 mm SOLANACEAE
Apium prostratum subsp. phillipii 2 mm APIACEAE
Aotus tietkensii
Argyroglottis turbinata
3 mm FABACEAE
10 mm ASTERACEAE 77
Australian Seeds
Aristida inaequiglumis
Asterolasia squamuligera
20 mm POACEAE
Arytera divaricata
6 mm SAPINDACEAE
Asteridea asteroides
7 mm ASTERACEAE
4 mm RUTACEAE
Astrebla lappacea
5 mm POACEAE
Astroloma foliosum
6 mm ERICACEAE
Atalaya hemiglauca
5 mm SAPINDACEAE
Atriplex semilunaris
4 mm CHENOPODIACEAE
78
Atriplex lindleyi subsp. inflata 2 mm CHENOPODIACEAE
Atriplex nummularia
3 mm CHENOPODIACEAE
Atriplex spongiosa
Atriplex vesicaria
4 mm CHENOPODIACEAE
2 mm CHENOPODIACEAE
Australian Seeds
Austrodantharia caespitosa
2 mm POACEAE
Austrostipa scabra
3 mm POACEAE
Baeckea behrii
5 mm MYRTACEAE
Banksia attenuata
14 mm PROTEACEAE
Banksia audax
12 mm PROTEACEAE
Banksia baxteri
10 mm PROTEACEAE
Banksia blechnifolia
15 mm PROTEACEAE
Banksia brownii
11 mm PROTEACEAE
Banksia burdettii
10 mm PROTEACEAE
Banksia caleyi
14 mm PROTEACEAE
Banksia coccinea
5 mm PROTEACEAE
Banksia cuneata
5 mm PROTEACEAE 79
Australian Seeds
Banksia dryandroides
13 mm PROTEACEAE
Banksia elderiana
11 mm PROTEACEAE
Banksia elegans
5 mm PROTEACEAE
Banksia gardneri
15 mm PROTEACEAE
Banksia goodii
16 mm PROTEACEAE
Banksia grandis
15 mm PROTEACEAE
Banksia hookeriana
12 mm PROTEACEAE
Banksia laevigata subsp. fuscolutea
9 mm PROTEACEAE
Banksia laevigata subsp. laevigata
15 mm PROTEACEAE
Banksia laricina
12 mm PROTEACEAE
Banksia lemanniana
14 mm PROTEACEAE
Banksia leptophylla
18 mm PROTEACEAE
80
Australian Seeds
Banksia lindleyana
10 mm PROTEACEAE
Banksia lullfitzii
7 mm PROTEACEAE
Banksia menziesii
12 mm PROTEACEAE
Banksia nutans
13 mm PROTEACEAE
Banksia occidentalis subsp. occidentalis
7 mm PROTEACEAE
Banksia occidentalis subsp. formosa
11 mm PROTEACEAE
Banksia oreophila
12 mm PROTEACEAE
Banksia praemorsa
10 mm PROTEACEAE
Banksia prionotes
6 mm PROTEACEAE
Banksia pulchella
10 mm PROTEACEAE
Banksia quercifolia
9 mm PROTEACEAE
Banksia sceptrum
13 mm PROTEACEAE 81
Australian Seeds
Banksia solandri
14 mm PROTEACEAE
Banksia sphaerocarpa var. sphaerocarpa
10 mm PROTEACEAE
Banksia sphaerocarpa var. dolichostyla
8 mm PROTEACEAE
Banksia tricuspis
15 mm PROTEACEAE
Banksia verticillata
12 mm PROTEACEAE
Banksia victoriae
10 mm PROTEACEAE
Banksia violacea
14 mm PROTEACEAE
Bauhinia cunninghamii
Beaufortia eriocephala
82
1 mm MYRTACEAE
Beaufortia interstans
15 mm FABACEAE
Beaufortia elegans
1 mm MYRTACEAE
1 mm MYRTACEAE
Beaufortia orbifolia
1.5 mm MYRTACEAE
Australian Seeds
Billardiera floribunda
Bonamia pannosa
2 mm PITTOSPORACEAE
2.5 mm CONVOLVULACEAE
Billardiera fraseri
Bonamia rosea
Boronia alata
3 mm RUTACEAE
Boronia crenulata
Boronia revoluta
3.5 mm RUTACEAE
Borya nitida
4 mm PITTOSPORACEAE
2.5 mm CONVOLVULACEAE
2 mm RUTACEAE
0.5 mm BORYACEAE
Billardiera heterophylla
2 mm PITTOSPORACEAE
Boronia adamsiana
2 mm RUTACEAE
Boronia exilis
1.5 mm RUTACEAE
Bossiaea aquifolium
4 mm FABACEAE 83
Australian Seeds
Bossiaea bossiaeoides
4 mm FABACEAE
Bossiaea linophylla
Bossiaea spinescens
3 mm FABACEAE
Brachychiton diversifolius
Brachyscome cheilocarpa
Brunonia australis
84
1.5 mm ASTERACEAE
2 mm GOODENIACEAE
Brachyscome ciliaris
Buchnera ramosissima
2 mm FABACEAE
3 mm FABACEAE
Bossiaea ornata
10 mm MALVACEAE
Brachyscome bellidioides
1 mm ASTERACEAE
2 mm ASTERACEAE
Brachyscome lineariloba
2.5 mm ASTERACEAE
0.5 mm OROBANCHACEAE
Bulbine semibarbata
2 mm ASPHODELACEAE
Australian Seeds
Burchardia conjesta
2 mm COLCHICACEAE
Caladenia arenicola