Analysis of geographic and taxonomic groups informs conservation of Rhododendron subgenus Vireya (Ericaceae)

Although Rhododendron subg. Vireya, comprising 400 taxa, is one of the largest plant genera in Southeast Asia, with taxa found throughout the region, it has a significant conservation problem, with conservation status assessments in 2011 and 2015 placing 201 taxa in an IUCN Red List threat category. Plant conservation is driven by the Global Strategy for Plant Conservation, with Target 8 requiring 75 % of threatened plant taxa to be conserved in ex situ collections, by 2020. To date there has been limited analysis of conservation priorities for subg. Vireya, or any consideration of how its geographic characteristics, complex taxonomy, and existing ex situ collections might influence priorities. We analyse the IUCN Red List status of geographic origins and taxonomic sections within Rhododendron subg. Vireya, then determine the representation of those groups in cultivation in New Zealand and selected international collections. Using a set of 'Red List' and 'not in cultivation' factors, our analysis shows that geographic origins New Guinea, Sumatra and Sulawesi, and taxonomic sections Schistanthe: malesia, Schistanthe: euvireya, and Hadranthe (Phaeovireya) should have priority for both in situ and ex situ conservation. Of the 400 taxa, 245 (61 %) are in cultivation, and of the 201 Red List taxa, 80 (40 %) are in cultivation. Wild-source material is held for 218 taxa, including 66 Red List taxa. These analyses provide baseline data for development of a conservation strategy for Rhododendron subg. Vireya, and we propose six actions that should be included in that strategy.