Gastrochilus immaculatus (Orchidaceae, Epidendroideae), a new epiphytic orchid from Chongqing, Southwest China

Gastrochilus immaculatus (Orchidaceae) is described and illustrated as a new species from Chongqing, southwestern China, where it grows epiphytically on tree trunks or rock walls in evergreen broad-leaved forests. It differs from the morphologically similar G. fargesii by its shorter stems, broader falcate-oblong leaves, and, especially, its golden-yellow immaculate flowers with a rather acute apex of the hypochile. Phylogenetic analyses based on nuclear ITS and four chloroplast markers ( mat K, psb A– trn H, psb M– trn D, and trn L–F) strongly support it as a sister species of G. fargesii within G. sect. Acinacifolii . Only three small subpopulations were discovered within a scenic spot in a deep limestone valley in southern Chongqing, warranting a preliminary IUCN classification of Critically Endangered (CR). This discovery also highlights the overlooked epiphytic orchid diversity along the mountain ranges surrounding the Sichuan Basin.