New Zealand collections of Rhododendron as a resource for ex situ conservation

This study uses Rhododendron L. collections in New Zealand to analyse the contribution of introduced species in cultivation to global ex situ conservation. Living botanical collections of Red List taxa are the fundamental resource that enable ex situ conservation, and Target 8 of the Global Strategy for Plant Conservation requires 75% of Red List taxa to be in ex situ collections by 2020. We compared Rhododendron taxa (species, subspecies, botanical varieties) in New Zealand with the range of taxa in international cultivation, and determined the presence of taxa from Red List categories, geographic origins and taxonomic groups. The 566 taxa in New Zealand, including 224 Red List taxa, encompass 67% of the taxa in cultivation worldwide, ranking second internationally for number of taxa in the collections investigated. New Zealand holds wild-collected material of 230 taxa, including 70 Red List taxa, and 20 taxa for which wild material is not listed in the international collections studied. China is the geographic origin of the greatest number of Rhododendron Red List taxa held in New Zealand. Of the 77 taxonomic subsections of Rhododendron, New Zealand holds 75% or more of the taxa in cultivation for 37 subsections, and 75% or more of the Red List taxa in cultivation for 24 subsections. The greatest numbers of Red List taxa in New Zealand collections are from section Rhododendron subsection Maddenia (20) and section Pontica subsection Neriiflora (17). Our analysis enables us to (1) propose conservation action for Rhododendron in New Zealand, (2) summarise our approach as a model for examining other introduced plant genera in New Zealand, and (3) propose our method as a component of an ex situ conservation strategy for New Zealand.