Platanthera xizangensis (Orchidaceae, Orchideae), a new species from Southeast Xizang, China

A new species, Platanthera xizangensis, discovered in Motuo county, Xizang Autonomous Region, China is described and illustrated. This species is close to P. milinensis by sharing greenish and spurless flowers, but is readily distinguished from the latter by presence of two subopposite leaves, lax subsecund inflorescence and lip with calli at base. Molecular phylogenetic analyses based on three DNA markers (nrITS, matK, rbcL) revealed that P. xizangensis is sister to P. milinensis with high support. Key to the Platanthera species in the Pan-Himalaya is also provided.