Rhododendron mulunense (Ericaceae), a new species from the karst mountains of Guangxi and Guizhou provinces, China

<i>Rhododendron mulunense</i>, a new species of <i>Rhododendron</i> (Ericaceae) within subsect. Maddenia in sect. Rhododendron and endemic to karst areas of Guangxi and Guizhou Province, SW China, is described and illustrated. The new species most closely resembles <i>R. wumingense</i>, particularly in scale density on the abaxial leaf surface and in flower color and shape, but can be readily distinguished by its hairless shoots and leaves, larger tubular-funneled corolla, and longer and thinner white tube flushed with pink. According to the IUCN Red List Categories and Criteria, the threatened status of the new species is assessed as "Endangered, EN C2a(i), D." We provide detailed documentation of its morphological characteristics, geographical distribution, digitized holotype voucher, and comparative photographs, along with a diagnostic table. An identification key is provided as a primary tool to enable taxonomic discrimination of this species from its congeners.