Elymus chaobotryus (Poaceae), a new species from the north-eastern Qinghai-Tibetan Plateau, China.

Elymus chaobotryus Y.C. Zhang, sp. nov. (Poaceae, Triticeae) from the north-eastern Qinghai-Tibetan Plateau (Tongren City, southeastern Qinghai, China) is described and illustrated based on detailed morphological comparisons and complete plastome data. The new species is readily distinguished from morphologically similar taxa by its pendulous compound spike 16-19 cm long, bearing 10-15 short lateral branches (2-4 cm) produced from nearly all nodes of the main rachis; the branches become progressively longer toward the base, giving the inflorescence a characteristic grape-like appearance. It further differs in having lanceolate glumes 3-4 mm long with mucros (< 0.9 mm), lanceolate lemmas 5-7 mm long with awns (3-4 mm), and conspicuously narrow leaf blades (2-5 mm wide). Flow-cytometric analysis estimated a genome size of 11.43 Gb, while chromosome and cytogenetic analyses confirmed a hexaploid chromosome complement (2n = 6x = 42) and were consistent with an StHY genomic constitution. In plastome-based phylogenetic analyses, E. chaobotryus is placed within the broader Elymus complex and is recovered as sister to E. dahuricus.