Geographic analysis of Red List Rhododendron (Ericaceae) taxa by country of origin identifies priorities for ex situ conservation

A Red List assessment is insufficient to determine priorities for ex situ conservation in large genera such as Rhododendron, where there may be hundreds of taxa in any one Red List category. We have utilised an analysis of the geographic origins of 1?215 taxa of Rhododendron (Ericaceae) as a method to prioritise Red List taxa for ex situ conservation. This analysis includes descriptions of distribution and endemism by country of origin, analysis of the incidence of the 715 Red List taxa by country of origin, and determination of the extent to which taxa from each country of origin are in cultivation. We determined that of 30 countries of origin and a ‘Europe’ aggregate, 24 origins contain Red List taxa. Of those 24 origins, 17 origins and ‘Europe’ have greater than 75 % of Red List taxa ‘in cultivation’, as defined in this study, so that Target 8 of the Global Strategy for Plant Conservation has theoretically been met. However, for some of these origins the number of each taxon held ‘in cultivation’ is very low and genetic diversity is likely to be poor. The remaining six countries of origin have less than 75 % of Red List Rhododendron taxa recorded ‘in cultivation’ (Indonesia (28 %), Papua New Guinea (29 %), Malaysia (59 %), China (60 %), Japan (62 %) and Solomon Islands (0 %)). Analysis of a set of Red List factors and ‘not in cultivation’ factors reveals that Red List taxa from Indonesia, China and Papua New Guinea should take priority for ex situ conservation