582 L. Hu et al.


TABLE 2 Rhododendron ss. Maddenia taxa that lack wild collections, categorized as not in cultivation, in cultivation but with no wild-source accessions, and in cultivation with wild-source accessions of unknown provenance (not mapped in Fig. 1b). These taxa require either fur- ther wild collection or investigation regarding the origins of the wild collections.


Taxon (by status)


Not in cultivation R. amandum


R. yaogangxianense R. yizhangense


R. vanderbiltianum R. yungchangense R. × carvori R. basfordii R. eheinense R. grothausii


R. rubrantherum


R. sinonuttallii R. linearilobum R. rhombifolium R. carneum


R. iteophyllum Country of origin IUCN Red List category1


China China China


Indonesia China


Bhutan China


China, Bhutan Myanmar


In cultivation, no wild-source accessions R. roseatum


Myanmar India


R. pseudomaddenii


India China China China India India


DD DD DD LC LC NE NE NE NE NE


China, Myanmar VU China China China


VU CR CR NE NE


In cultivation, wild-source accessions of unknown provenance R. coxianum R. kiangsiense R. taronense R. levinei R. parryae


CR NT VU DD LC LC


Number of wild sources Number of living collections


0 0 0 0 0 0 0 0 0 0


0 0 0 0 0 0


1 1 1 4 1 1


1DD, Data Deficient; LC, Least Concern; NE, Not Evaluated; VU, Vulnerable; CR, Critically Endangered.


on site (IUCN Nepal, 2010; DoFSC, 2019; Namgay&Sridith, 2021). Nevertheless, our results can be utilized by global databases or organizations such as the Global Tree Assess- ment (BGCI, 2021a), World Flora Online and Global Conservation Consortium for Rhododendron. Although it is the largest global plant conservation network, the data- bases of BGCI do not cover all ex situ collections (Table 1). Gardens not in the BGCI GardenSearch data- base are probably not reporting collection data to BGCI, in- cluding the private gardens in New Zealand that hold Rhododendron collections.


Knowledge gaps in assessing genetic representation of ex situ collections of Rhododendron


A globally updated taxon list is a necessary basis for study- ing biodiversity. Complex taxonomy is a problematic fea- ture of big genera (Frodin, 2004) such as Rhododendron. For example, the unresolved taxonomy of ss. Maddenia spe- cies remains a significant challenge for their conservation assessment; nine of the 20 threatened or at risk taxa were described as being under taxonomic debate in Gibbs et al. (2011). In addition, new taxa may have been proposed based on morphological observations but have not yet


been officially published, such as R. valentinioides (Supplementary Material 3). In our analysis we included wild accessions of infraspecific taxa and affinities, as we considered their variation part of the diversity within a species. However, the contribution of these accessions to the genetic representation of relevant species can only be examined realistically based on determined taxonomic status. Conservation assessments also require further work.


Field investigation is needed for Data Deficient taxa (e.g. R. formosum var. inaequale) in the previous Red List of Rhododendrons (Gibbs et al., 2011), or updates are needed for taxa that are to be re-evaluated. Global and regional (e.g. China, India) conservation status could affect decision- making at different administrative levels. Recent surveys of the wild populations of threatened Rhododendron species (Ma et al., 2014), updates of China’s Red Lists (Qin & Zhao, 2017; Qin et al., 2017) together with upcoming assess- ments coordinated by BGCI would contribute to improving our understanding of the distribution of Rhododendron taxa and their conservation status. Wild populations of ss. Maddenia in their countries of


origin often lack investigations of both size and distribution. Our geo-mapping relied on information derived from pub- lished literature and databases, with varying levels of data


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


0 0 0 0 0 0 0 0 0 0


3 3 1 2 8 3


3 4 6 9 9 1


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