What to do when we can't bank on seeds: What botanic gardens can learn from the zoo community about conserving plants in living collections.

Species loss due to human activities is occurring at an unprecedented pace ( Barnosky et al., 2011 ), and over the last few decades, botanic gardens have responded by expanding their conservation activities ( CBD, 2010 ). Botanic gardens play a particularly critical role in the development of ex situ (off -site) collections of threatened plant species, and the botanic garden community has helped develop current best practices for ex situ conservation and reintroduction (e.g., via the Center for Plant Conservation; Guerrant et al., 2004 ). Th e majority of plant species are amenable to seed banking or at least vegetative propagation (horticultural or tissue culture), which allows them to be preserved for decades or even centuries before regeneration is necessary and before genetic and demographic viability become an issue ( Havens et al., 2004 ). Consequently, much of the research geared to support ex situ plant conservation has focused on understanding how to effi ciently capture wild genetic diversity to enable successful future reintroduction eff orts ( Guerrant et al., 2004 ). However for “exceptional” plant species that either do not produce seeds or produce seeds that are recalcitrant (i.e., desiccation intolerant so they cannot be dried and frozen), maintaining demographic viability and genetic diversity ex situ can be particularly challenging ( Pence, 2014 ). To date, less effort has been dedicated to ensuring that these living collections, once brought into ex situ cultivation, remain genetically diverse and demographically viable over the long term to support reintroduction eff orts (but see Havens et al., 2004 ). For many exceptional species, living plant collections are the only currently available ex situ conservation option, and the maintenance of these living collections introduces numerous genetic and demographic challenges associated with small, isolated populations. If not curated correctly, these small populations are subject to founder eff ects, genetic drift , and inbreeding, and can experience selective pressure from biotic and abiotic conditions in the ex situ environment. Th ese factors could compromise future reintroduction eff orts and ultimately lead to loss of the species from ex situ collections altogether. In the future, cryopreservation and/or tissue culture may be viable ex situ approaches for exceptional species, thus minimizing immediate concerns about genetic and demographic losses. However, the techniques required for these alternative germplasm conservation approaches are oft en species-specifi c and currently unavailable for many threatened species ( Pence, 2014 ). In addition, capacity and resources to develop and maintain cryopreservation protocols is limited or lacking in many regions. Until research and resources reach a point where all exceptional species can be cryopreserved, living collection management will continue to be critical. Despite the value of ex situ collections, some threatened plant species and valuable genetic resources have already been lost from botanical collections ( Govaerts, 2010 ). Of 844 plant taxa identifi ed as extinct in the wild in 2010, 9% were curated in collections, while another 5% had been in collections but subsequently lost ( Govaerts, 2010 ). While the cause of these losses was not reported, it is likely that at least some were the result of genetic or demographic collapse. It is clear that an integrated and more collaborative approach is needed to eff ectively conserve threatened species ex situ. For example, Brighamia insignis (Campanulaceae), an endemic Hawaiian succulent species, is functionally extinct in the wild with only one remaining extant individual. It is cultivated ex situ in at least 57 botanical collections around the world, but in need of an integrated management plan. Th is species can be seed banked, but seeds lose 1 Manuscript received 30 June 2016; revision accepted 15 August 2016. 2 Department of Plant Science and Conservation, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois 60035 USA; 3 Department of Science and Conservation, National Tropical Botanical Garden, 3530 Papalina Road, Kalāheo, Hawai‘i 96741 USA; 4 Department of Conservation Science, Chicago Zoological Society, Brookfi eld, Illinois 60513 USA; 5 International Center for Tropical Botany, Florida International University and the National Tropical Botanic Garden, Th e Kampong, 4013 South Douglas Road, Coconut Grove, Florida 33133 USA; and 6 Botanic Gardens Conservation International, 199 Kew Road, Richmond, Surrey TW9 3BW UK 7 Author for correspondence (e-mail: [email protected]) doi:10.3732/ajb.1600247 O N T H E N AT U R E O F T H I N G S : E S S AY S New Ideas and Directions in Botany