Rhododendron griersonianum Balf. f. et Forrest, belonging to subsection Griersoniana Davidian ex Chamb of the Ericaceae, is a Critically Endangered species on T he Red List of Rhododendron s (Gibbs et al., 2011, Botanic Gardens Conservation International) and the Threatened Species List of China's Higher Plants (Qin et al., 2017, Biodiversity Science, 25, 696–744). Circa 10% of all registered Rhododendron cultivars have been created by hybridization with R. griersonianum. Despite its value for horticulture, the conservation of R. griersonianum has been afforded little attention. After its description in 1919 (Isaac Bayley & Gorge, 1919, Notes from the Royal Botanic Garden, Edinburgh, 11, 69–71), Gorge Forrest collected the species again in 1924, 1925 and 1931. In 1964 Wu Sugong of Kunming Institute of Botany, Chinese Academy of Sciences, collected one specimen, deposited in the Herbarium of Kunming Institute of Botany, Chinese Academy of Sciences. Since then the species had not, until now, been located again.
To secure up-to-date information on R. griersonianum we surveyed in its type locality during its flowering time in May 2015, but failed to find the species. In May 2016, however, with the help of local people, we surveyed again and three plants with flowers were found within an area of c. 100 m2 on steep rocky terrrain near farmland in Jietou, Tengchong County, west Yunnan. Following further searches we found four plants on a riverbed in Houqiao, c. 50 km from the first population. In July 2018 we found eight plants along a road in Guyong, c. 12 km from the first population and c. 42 km from the second population. We did not find seedlings in any of the three populations. Information obtained from interviews with local people and our field investigations indicated that the main threat to this species is the loss of suitable habitat as a result of human activities such as logging, farming, and reservoir and road construction.
Priority conservation action is required to prevent the extinction of this Critically Endangered and horticulturally important species. At Kunming Botanical Garden of Kunming Institute of Botany seedlings are being propagated, from both seeds and cuttings, for ex situ conservation, a local nature reserve has agreed to establish protection plots in the habitat of R. griersonianum for in situ conservation, and samples have been taken for phylogenetic research. In addition, further surveys to locate other potential populations are required. An integrated conservation action plan for the species is now being prepared.
