Rhododendron conservation in botanic gardens 581


FIG.2 Rhododendron subsection Maddenia in ex situ conservation. (a) The 73 global ex situ sites of living collections. (b) The number of ex situ sites and living collections in countries of ex situ conservation.


subsection, and seven of these Data Deficient taxa are represented by no or fewer than three wild accessions. For threatened and Data Deficient taxa, targeted fieldwork and data collection should be undertaken. In addition, some of the 10 taxa not in cultivation (three Data Deficient, two Least Concern and five Not Evaluated; Table 2) await further investigation to confirm their conservation status. Mapping of the wild collections showed similar hotspots


to the wild distribution of ss. Maddenia (Fig. 1), indicating a relatively adequate ecogeographical representation of ex situ living collections. However, the distribution may not have been well sampled for individual taxa. For example, although Rhododendron leptocladon is native to the China–Viet Nam border and categorized as Vulnerable glo- bally, its wild populations are still under examination (Data Deficient in China), and current wild accessions have only been collected from northern Viet Nam (Supplementary Material 3). In addition, the ecogeographical representation of ex situ collections could reflect collector bias and limita- tions as a result of administrative boundaries. Under legislation such as the Nagoya Protocol (CBD, 2011), field expeditions, species introductions and plant material exchanges may become less frequent because of local


restrictions, which highlights the need to determine the wild diversity in existing living collections. Globally, ex situ collections of ss. Maddenia are wide-


spread over countries in both the Northern and Southern Hemispheres but rare in their countries of origin (Fig. 2b; Table 1). Sharrock (2020) noted this trend for threa- tened species, and this is not unique to Rhododendron but also occurs in other plant groups such as Magnolia (Magnoliaceae; Linsky et al., 2022)and Zelkova (Ulmaceae; Kozlowski et al., 2012). Considering the small number of botanic gardens in countries of origin that report to BGCI (Table 1), ex situ collections in these countries may not be well covered by our study. However, although lacking published data on ex situ collections, countries of origin may be active regarding in situ conservation. In China, the country of origin of the greatest number of ss. Maddenia taxa, additional data on ex situ collections of Rhododendron (Ericaceae) have been published (Wang, 2022) from the Ex Situ Flora of China project (Huang et al., 2017). In India, plants of the Rhododendron formosum complex are under on-site observation in Meghalaya (Mao et al., 2017). Conservation policies in Nepal and Bhutan also indicate that Rhododendron species are more likely to be protected


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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