The Tip of the Iceberg: What We Know and Don’t Know About Exceptional Plants

Valerie Pence, Cincinnati Zoo & Botanical Garden

Plant species that, either through seed availability or physiology, are unable to be conserved and recovered using conventional seed banking practice have been designated as exceptional plants. A definition of exceptionality has recently been put forward, describing four factors that contribute to this condition, depending on what step in the seed banking process the roadblock occurs. Based on this definition, a Working List of Exceptional Plants has been created in a collaborative effort between several institutions to focus attention on, promote, and facilitate the conservation of these species. This list includes 775 species currently documented as exceptional. In addition, there are 17,603 species with some, but insufficient, data to suggest exceptional status, as well as 7,577 species that are threatened congeners of exceptional species, and both of these groups need to be prioritized for additional research. Finally, there are 5,152 species that are documented as known or probably non-exceptional. Based on the number of species predicted to be recalcitrant (at least ~28,000), which is only one of the four factors that can result in exceptionality, the Working List of Exceptional Plants highlights the immense gap in our knowledge of which species are exceptional. Only 20% of genera had one or more species that had been assessed for exceptionality. In order to fill this gap, information from field botanists and seed biologists is needed. The List will be available online and new and updated information can be submitted to the List. An understanding of which plant species are exceptional and the basis of their exceptionality is the first step in addressing the challenge of applying alternative ex situ conservation strategies to these species, which will include multi-institutional living collections and cryobanking. (This research was supported in part by a grant from the Institute of Museum and Library Services.)