Rhododendron conservation in botanic gardens 577


Volis, 2017; Chen & Sun, 2018; Hudson et al., 2021; Wei & Jiang, 2021). Using the number and provenance of wild accessions to


estimate the captured genetic diversity can inform future collection management (Beckman, 2019; Linsky et al., 2022). Current practice includes the concept of metacollec- tions to manage pooled collections in multiple botanic gardens, obtained from spatially separated populations with coordinated sampling internationally or regionally (Griffith et al., 2020; Westwood et al., 2021). Views differ on the number of wild accessions required to conserve sufficient genetic diversity of a species, but multiple wild samples should be collected from diverse populations, with each ex situ collection duplicated at multiple sites (Griffith et al., 2015; Ren et al., 2019; Zumwalde et al., 2022). Rhododendron is a big genus (i.e. one with 500 or more


species; Frodin, 2004)of$1,000 species across a wide geo- graphical range, with the greatest diversity extending from the southern Himalayas to south-west China (Gibbs et al., 2011; MacKay et al., 2018; Shrestha et al., 2018). Assessing the number and geographical range of Rhododendron populations in the wild is challenging because of their inaccessible habitats in montane or remote regions (Gibbs et al., 2011). Under the scope of BGCI, the Global Conservation Consortium for Rhododendron was estab- lished in 2018 to coordinate conservation action worldwide. Despite the large number of Rhododendron taxa conserved in botanic gardens (78% of threatened taxa in cultivation; MacKay & Hootman, 2018; MacKay et al., 2018) and ongoing ex situ conservation projects (Ma et al., 2014; McMeekin, 2022), the genetic representation of ex situ collections of Rhododendron species is seldom studied. Herewe present subsection (ss.)Maddenia as a case study


for the conservation of genetic diversity in global ex situ collections. Subsection Maddenia (subgenus Rhododendron, section Rhododendron) exhibits conservation issues that occur across the genus, including poorly known wild dis- tribution (Gibbs et al., 2011), complex taxonomy (Cubey, 2003;Donald, 2012;McMeekin, 2022; Hu et al., 2023), taxo- nomic debates over the conservation status of species (Gibbs et al., 2011; Li et al., 2018) and recently published species requiring field investigation (Chang et al., 2021; Rushforth et al., 2022).We analysed ecogeographical representation as a proxy for genetic representation in current wild collections of ss. Maddenia to identify ex situ conservation gaps for future action. Data from ex situ collections (at taxon and accession levels) together with taxon distribution are used to (1) update a checklist of taxa in the subsection including IUCN Red List assessment and wild distribution, (2)char- acterize the ex situ conservation status of taxa including presence or absence in cultivation and location and size of ex situ collections, (3) examine the ecogeographical represen- tation of wild-source accessions, and (4)identifygaps and derive conservation strategies.


Methods


Firstly,we compiled an updated checklist of all ss. Maddenia taxa. Secondly, we compiled two datasets for ss. Maddenia: (1) taxa in the wild, annotated by IUCN Red List cat- egory (IUCN, 2022), country/region of distribution and altitude of habitat; and (2) taxa in ex situ conservation, annotated by cultivation status (whether a taxon is in cultivation), location of global ex situ sites and number of living collections (taxon-level data; Supplementary Table 1), wild collection provenance and number of wild accessions per taxon (accession-level data; Supplementary Table 2). Thirdly, we formulated these data into a profile for each taxon in ss. Maddenia and used these to produce a map with known distribution and ex situ sites of living collec- tions plotted together with origins of wild accessions (Supplementary Material 1). Ex situ conservation gap ana- lysis was based on the compiled datasets. In this study,we defined taxa as in cultivation if therewas


a living collection recorded in any one of the data sources used. We defined a living collection as the record of a taxon with living plants cultivated in a botanic garden, and any one collection could include multiple accessions.


Checklist of subsection Maddenia


In the checklist, we based all taxa of ss. Maddenia (species, subspecies and botanical varieties) with their synonyms on Chamberlain et al. (1996), with updates from post-1996 studies (Argent et al., 2008; Gibbs et al., 2011; Donald, 2012; Mao & Bhaumik, 2015; Mao et al., 2017; MacKay et al., 2018; Rushforth & Nguyen, 2019; Chang et al., 2021; Rushforth et al., 2022). We initially obtained threatened categories of taxa from the IUCN Red List of Rhododen- drons (Gibbs et al., 2011) and from assessments for recently published species (Mao & Bhaumik, 2015; Chang et al., 2021). Additional sources were the published IUCN Red List assessments (IUCN, 2022) and national assessments of endemic species in China (MEP–CAS, 2013; Qin et al., 2017). We also indexed the BGCI Threat- Search database for existing conservation assessments (BGCI, 2022b). We mapped distributions and countries of origin for


each taxon using polygons based on geographical informa- tion from the literature and online databases (Cullen, 1980; Davidian, 1982; Feng, 1988, 1992; Feng & Yang, 1999;Fang et al., 2005, 2011; Gibbs et al., 2011; Mao & Bhaumik, 2015; Mao et al., 2017; RBGE, 2018a,b; Chang et al., 2021; GBIF, 2021; Rushforth et al., 2022). We georeferenced distribution data and generated maps using QGIS 3.20.3 (QGIS Development Team, 2021). We stacked polygons for each taxon to produce a species richness map. See Sup- plementary Material 1 for details of data processing and taxon information.


Oryx, 2024, 58(5), 576–586 © The Author(s), 2024. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324000759


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