Conserving orthodox seeds of globally threatened plants ex situ in the Millennium Seed Bank, Royal Botanic Gardens, Kew, UK: the status of seed collections

Ex situ seed storage underpins global agriculture and food supplies and enables the conservation of thousands of wild species of plants within national and international facilities. As an insurance policy against extinction, ex situ seed conservation is estimated to cost as little as 1% of in situ conservation. The assumptions, costs, risks and scientific challenges associated with ex situ plant conservation depend on the species, the methods employed and the desired storage time. Recent, relatively widespread evidence of less than expected longevity at conventional seed bank temperatures, innovations in the cryopreservation of recalcitrant-seeded species and economic comparators provide compelling evidence that ultra-cold storage should be adopted for the long-term conservation of plants. Policy instruments, such as the Global Strategy for Plant Conservation (2011-2020), should respond to the evidence base and promote the implementation of cryopreservation for both tropical and temperate plants.

Plants provide fundamental support systems for life on Earth and are the basis for all terrestrial ecosystems; a decline in plant diversity will be detrimental to all other groups of organisms including humans. Decline in plant diversity has been hard to quantify, due to the huge numbers of known and yet to be discovered species and the lack of an adequate baseline assessment of extinction risk against which to track changes. The biodiversity of many remote parts of the world remains poorly known, and the rate of new assessments of extinction risk for individual plant species approximates the rate at which new plant species are described. Thus the question ‘How threatened are plants?’ is still very difficult to answer accurately. While completing assessments for each species of plant remains a distant prospect, by assessing a randomly selected sample of species the Sampled Red List Index for Plants gives, for the first time, an accurate view of how threatened plants are across the world. It represents the first key phase of ongoing efforts to monitor the status of the world’s plants. More than 20% of plant species assessed are threatened with extinction, and the habitat with the most threatened species is overwhelmingly tropical rain forest, where the greatest threat to plants is anthropogenic habitat conversion, for arable and livestock agriculture, and harvesting of natural resources. Gymnosperms (e.g. conifers and cycads) are the most threatened group, while a third of plant species included in this study have yet to receive an assessment or are so poorly known that we cannot yet ascertain whether they are threatened or not. This study provides a baseline assessment from which trends in the status of plant biodiversity can be measured and periodically reassessed.