Callothamnus accidens grown from seeds in herbarium collection
Extinct Plants Project
The Herbarium of the Royal Botanic Gardens, Kew is at the forefront of plant taxonomic science. Eminent botanists, including George Bentham and W.A. Broomfield, donated their own collections to William Hooker’s Herbarium in 1877, marking the beginnings of the Kew Herbarium as we know it today. There are currently over seven million specimens in the Herbarium (the largest collection of historical plant specimens) representing nearly 98% of all plant genera in the world. The Kew Herbarium has the largest collection of historical plant specimens (including reference types) worldwide, collated from all regions and habitats around the world.
The Extinct Plant Database is a new resource documenting herbarium specimens of extinct taxa. During the development of the database, the potential for germinating seeds from these specimens was also investigated.
Seeds from some orthodox species (seeds which can withstand drying to low relative moisture content whilst retaining the ability to germinate) have the potential to remain viable for hundreds of years. This theory suggests that rare herbarium specimens collected from the wild decades ago could still be viable (Bowles 1993). Furthermore it has been suggested that viable seeds held within herbaria could be used to recover rare plant species. Within Bowles's 1993 publication there was successful germination of 97-year old seeds of Astragalus neglectus, removed from a specimen in the Northern Illinois University Herbarium. Likewise germination was reported in 237-year old seeds of Nelumbo nucifera from the British Museum of Natural History Herbarium following a flood during the bombing of London in the 2nd World War (Sculthorpe 1967).
Within the Kew Herbarium collections there are approximately 1000 specimen sheets for species which are known to have become extinct. To date these have not been systematically searched or collated into a useable resource for botanists. Many of these sheets may have seeds on them which are still able to germinate under the right conditions. The seeds on these specimens could therefore represent the only remaining viable tissue of the species. ‘Resurrecting’ such species could lead to opportunities for propagation and ex situ conservation or even repatriation of living plants. The seed material could also provide material for molecular analysis and investigations into plant evolution and causes of extinction.
To date only a small number of viable seeds have been recovered from specimens within the Kew Herbarium. One reason for this low number is that most of the characteristics of a plant that are used for identification are only apparent when the plants are in flowers. Botanists are less likely to take specimens when the plants are at the seed dispersal stage. Furthermore, even when seeds are present, the number of seeds is highly variable and most are unlikely to have the potential to germinate because the embryos are not fully mature or the seeds are severely damaged. The project has so far found nine species with seed suitable for germination trials. One species has had successful germination and is currently being propagated in the Wakehurst place gardens. This species is Callothamnus accidens (Myrtaceae; see database photographs for more information).
- Bowles et al. 1993. Propagation of rare plants from historic seed collections: Implications for species restoration and herbarium management. Restoration Ecology 1, 101-106.
Sculthorpe, C.D. 1967. The biology of aquatic vascular plants. Edward Arnold, London.
- Walters, C. et al. 2006.The utility of aged seeds in DNA banks. Seed science and Research 16 169-178.
- Lledo, M.D. et al. 1996. Micro propagation of Limonium thiniense Erben using herbarium material. Botanic Garden Mircropropagation News. Volume 1 Part 2.
Seed Conservation Department
Jennifer Dawson CBSCS
Dr Fiona R Hay
Dr Robin J Probert
Dr Paul Smith
Dr William Milliken
All specimen sheets for extinct species have been located and scanned / digitised on Herbcat/TOAD databases. The following plant families were targeted: Acanthaceae, Aizoaceae, Alliaceae, Amaryllidaceae, Boraginaceae, Burmanniaceae, Cactaceae, Compositae, Convolvulaceae, Cruciferae, Cupressaceae, Ericaceae, Euphorbiaceae, Gramineae, Hyacinthaceae, Hydatellaceae, Hydrocharitaceae, Iridaceae, Labiatae, Leguminosae, Lycopodiaceae, Musaceae, Myrtaceae, Pandanaceae, Polygonaceae, Pandanaceae, Ophioglossaceae, Rutaceae, Sapotaceae, Selaginellaceae, Woodsiaceae and Thelypteridaceae.
Fact Sheet Fusion software was used to produce a searchable database of extinct taxa in the Herbarium.
Specimens which include a number of seeds that appear mature were set aside. These specimens were used to then approach the appropriate Herbarium Curator to see if it was acceptable to remove a sample of the seeds for viability testing.
At the Millennium Seed Bank, digital photos were taken of all seeds under the microscope. Images were attached to the scanned images in Herbcat. Photos were also taken at other stages of the germination test. i.e. after imbibition and before possible disposal (if dead) or transplanting by the nursery (if viable).
Seeds were imbibed over distilled water for 24–48 hours at 20ºC (depending on seed size). Some seeds required mechanical scarification prior to imbibition. The Seed Bank Database was consulted to see if this and/or other dormancy-breaking treatments might be a characteristic of the family. The seeds were then placed on 1% distilled water agar in individual 10mm diameter wells of 125 × 85 × 20 mm (H × W × D) Multidish culture plates or larger 50mm or 90mm diameter Petri dishes or sandwich boxes, as appropriate, and placed in a temperature controlled incubator (temperature informed by the Seed Bank Database). Seeds were checked regularly for germination. If there was no germination after 12 weeks, the health of the seeds was evaluated by gentle pressure. If still firm, the seeds were left, perhaps with an adjustment to the germination conditions used. N.B. seeds that have been imbibed will not be returned to specimen sheets. Dead seeds were treated as waste and sterilised.
If there were any signs of seed germination, Wakehurst Place glasshouse staff were alerted and seedlings passed on for potting-up and propagation.