Rhododendron jiucaipingensis (Ericaceae), a new species from Guizhou, China

Rhododendron jiucaipingensis Jian Xu & M. T. An, sp. nov. (Ericaceae), a new species of R. subgen. Hymenanthes, subsect. Argyrophylla, from northwestern Guizhou, China, is described and illustrated. It is an evergreen shrub 1.5-3.0 m tall, characterized by green, densely white-tomentose current-year branchlets, leaves crowded at branch apices (5.5-9.5 × 2.5-4.0 cm) with 8-11 pairs of lateral veins, 10 stamens, and cylindric capsules 1.2-2.0 cm long. The new species is morphologically most similar to R. hypoglaucum and R. argyrophyllum, but it is readily distinguished by having densely white-tomentose current-year branchlets, fewer lateral veins (8-11 pairs), a double-layered white indumentum on the abaxial surfaces of young leaves, and 10 stamens. Phylogenetic analysis based on a whole-genome SNP dataset robustly resolves R. jiucaipingensis as a distinct lineage within subsect. Argyrophylla, positioned as sister to the monophyletic clade of five congeneric species with high support (SH-aLRT = 100%, UFBoot = 100%). This molecular evidence, congruent with diagnostic morphological characters, supports the recognition of R. jiucaipingensis as a species new to science.