Abstract: Elymus L. is the largest genus in the tribe Triticeae Dumort., encompassing approximately 150 species over the world. Species of the genus are widely distributed in the temperate regions, particularly in the northern hemisphere. China is one of the most important world’s distribution and diversification centers of the Elymus species, with more than 80 taxa (including those classifted in the genus Roegneria C. Koch) widely occurring in many provinces, particularly in the western and northern regions of the country. Owing to its abundance in species, extensive distribution, variable habitats, and complicated morphological variation, taxonomic classification of this genus has been always problematic. In addition, many traditional taxonomists from different parts of the world mainly had their research interests in their own regions due to historical reasons, which largely hampered communication between the regions. As a consequence, some Elymus species were described as new species several times by different taxonomists. The present paper reports taxonomic revision of two common Elymus species, i.e.E. antiquus and E. burchan-buddae. Elymus antiquus is a perennial and tetraploid (2n= 4x= 28) species containing the StStYY genomes. It is commonly found in western and northwestern China and is also found in mountain area of Nepal. This species was first described by a Russian agrostologist, S. A. Nevski, based on specimens collected from Tibet, China. Our study indicated that two grass species described as Agropyron microlepis Melderis from Nepal and Roegneria parvigluma Keng from Kangding of Sichuan are the synonyms of E. antiquus. Elymus burchan-buddae is also a perennial and tetraploid (2n = 4x = 28) species containing the StStYY genomes. It is widely distributed in western and northwestern China and might have its distribution in Nepal and northern India. This species was first described by Nevski based on specimens collected from Burchan Budai Shan (Kunlun Mountain) in Qinghai. Our investigation concluded that two species described as Agropyron nutans Keng from Xiahe of Gansu and Agropyron breviglumis Keng from Shao Wu Shi of Sichuan are the synonyms of E. burchan-buddae.

Key words: Triticeae, Elymus, Roegneria, Agropyron, Taxonomic revision, Morphology