Rhododendron diversity conservation in global botanic gardens: A case study of Maddenia species

Abstract

Effective ex situ conservation of plants in botanic gardens requires sufficient wild accessions to represent wild diversity. In Rhododendron L. (Ericaceae), c. 64% of the taxa are threatened or require field investigation. As a case study of the analysis of ex situ conservation gaps we used ecogeographical representation as a proxy for genetic representation in ex situ collections of the 65 taxa of Rhododendron subsection Maddenia. We compiled the first list profiling both wild distributions and ex situ wild collections of all taxa in subsection Maddenia. Our results reveal that 55 Maddenia taxa are in cultivation. Of the 18 threatened taxa all are in cultivation but nine require further collection to capture adequate wild diversity. There are 12 Data Deficient taxa: These await further field investigation of wild populations and nine of them require wild collections to conserve genetic diversity. The UK, the USA, Australia, New Zealand and China are the top five countries holding ex situ collections of subsection Maddenia; in these countries nearly 66% of the ex situ sites hold > 86% of the global living collections of subsection Maddenia. We recommend that wild collections of endemic species of subsection Maddenia should be established in all 10 countries of origin and that data should be shared internationally for metacollections. In addition to proposing priorities, our case study highlights the challenges facing data and collection management to help achieve effective ex situ conservation for Rhododendron species.