578 L. Hu et al.


Presence of subsection Maddenia in ex situ living collections


We collected data describing the presence of ss. Maddenia taxa in cultivation from three key sources. Firstly, we used the BGCI PlantSearch database (BGCI, 2021b) as the primary indicator of presence in cultivation. However, the public website PlantSearch only presents occurrence of taxa and not the location or number of ex situ collections. Therefore, we used an unpublished set of BGCI data (BGCI, 2020)that includes all Rhododendron records from GardenSearch and PlantSearch databases as the second source. We com- piled taxon-level collections data for ss. Maddenia in global botanic gardens from these two sources (Supplementary Table 1). We used the unpublished BGCI data (BGCI, 2020) and BGCI GardenSearch database (BGCI, 2022a)to identify ex situ collections held in countries worldwide. The third source was accession-level data from seven gardens in New Zealand, a hotspot of ex situ conservation of ss. Maddenia, and the seven largest collections of ss. Maddenia outside New Zealand. Data from the third source included unpublished data from MacKay et al. (2018) and additional data or individual garden updates from 2020. We have compiled accession-level data from the third source in Supplementary Table 2.


Provenance and number of wild accessions


To evaluate the ecogeographical representation of ss. Maddenia conserved ex situ, we collated provenance and number of accessions of wild collections in the 14 botanic gardens from the third data source. We analysed the data for each taxon. Determinants for our evaluation of conser- vation were number of wild collections (identified by the unique Collector ID for each wild collection), number of wild accessions per collection (identified by accessions un- der the same Collector ID), cultivation source material, Collector ID and provenance (habitat location or coordi- nates and altitude) ofwild accessions (SupplementaryTable 2). We mapped wild accessions of each taxon with docu-


mented coordinates in QGIS.When a wild accessionwas de- scribed from a certain location but without coordinates, we assigned the location around the centre of the geographical area, with the habitat and altitude of the taxon cross- referenced. When an accession was noted as from the wild but without provenance information, we considered it as a wild accession but did not plot it on the map.


Results


Checklist of subsection Maddenia The checklist reveals 65 taxa in Rhododendron ss. Maddenia, and we compiled a profile for each taxon (Supplementary


Material 3). Information on conservation status and wild distribution are included in each profile. The checklist in- cludes 18 threatened taxa (three Critically Endangered, two Endangered, 13 Vulnerable), four Near Threatened, 12 Data Deficient, 20 Least Concern and 11 Not Evaluated. Subsection Maddenia spans 10 countries across southern Asia (China, Myanmar, India, Viet Nam, Bhutan, Thailand, Nepal, Laos, Bangladesh and Indonesia; Fig. 1a; Table 1). China has the greatest number of native taxa (45), followed by Myanmar (20)and India(19). The mountainous areas in the China–north-east India and China–Myanmar borders are the geographical hotspots for this subsection.


Ex situ living collections per taxon by IUCN Red List category


We summarized numbers of ex situ sites and countries per taxon and classified them by Red List category (Supplementary Fig. 1a). All threatened (Critically En- dangered, Endangered, Vulnerable) and Near Threatened taxa are conserved in at least three botanic gardens. However, the 12 Data Deficient taxa have poorer repre- sentation: three (Rhododendron amandum, Rhododendron yaogangxianense, Rhododendron yizhangense)are not in cultivation and four (Rhododendron kuomeianum, Rhododendron linearilobum, Rhododendron rhombifolium, Rhododendron valentinioides (ined.)) are cultivated in only one or two botanic gardens. Least Concern taxa are well rep- resented, with only four of the 20 taxa not in cultivation or held in fewer than three botanic gardens.


Ex situ living collections in native and other countries


We identified 592 collection records of the 55 taxa in cul- tivation at 73 ex situ sites in 17 countries (Fig. 2; Supplementary Fig. 1; Supplementary Table 1). Ten taxa are not in cultivation (Table 2). Ex situ collections of ss. Maddenia are widely cultivated in Europe, North America, Southeast Asia and Oceania. There were no re- cords in Africa or South America (Fig. 2a). The UK, the USA, Australia, New Zealand and China are the top five countries holding ex situ collections of ss. Maddenia (Fig. 2b), where nearly 66% of the ex situ sites hold .86% of the living collections. Although a smaller num- ber of ex situ collections are conserved in Canada, Bel- gium and France, the remaining nine countries hold only c. 6% of the ex situ collections of this subsection, either at one ex situ site or with one collection record. Amongst the countries of origin, only China had ex situ


collections of ss. Maddenia reported to BGCI, with 32 collec- tions representing 22 taxa at five sites (Supplementary Table 1). There was no ex situ collection of ss. Maddenia re- corded in the other nine native countries. Using the BGCI GardenSearch database, several botanic gardens were


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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