Global List of Threatened Exceptional Plants A Working List of Exceptional Plant Species Coming soon! A working list of exceptional plant species. An initial list of threatened and non-threatened exceptional plants is being been compiled by comparing the species listed in Botanic Gardens Conservation International’s ThreatSearch database with species listed by the Royal Botanic Gardens Kew’s Seed Information Database. Beyond this, information has been provided by researchers on species known to lack accessible seeds, or to be recalcitrant, cold-sensitive, or short-lived, as reported by Helm Wallace (2015). We are interested in both threatened and non-threatened exceptional species, since work with non-threatened species can often inform work with threatened species.