Abstract
A new species, Koenigia bingchachaensis Bo Xu & H. Sun (Polygonaceae), is described and illustrated based on material from the alpine subnival of Zayü County, Xizang, China. The species is characterized by a perennial tufted habit, extensively developed braided-fissured rhizomes, numerous simple spreading stems, prominently petiolate (1.5-4.0 cm) and arched leaves, and paniculate inflorescences borne both terminal and axillary with a short, twisted rachis. Morphologically, it is closely allied to K. tortuosa and K. hookeri, but can be readily distinguished from both by a stable combination of vegetative and reproductive characters. Molecular phylogenetic analyses based on complete plastome and nuclear ribosomal ITS sequences strongly support K. bingchachaensis as a distinct species, resolving it as a well-supported sister lineage to the clade comprising K. hookeri and K. tortuosa. The integrative taxonomic approach, combining detailed morphology with molecular data, unequivocally confirms the specific status of K. bingchachaensis. The discovery expands the known diversity of Koenigia and highlights the potential for uncovering unique plant lineages in the extreme alpine environments of the Qinghai-Tibet Plateau.