Abstract: We have classified 11 species recently recognized as belonging to the genus Elymus into a resurrected and legitimate genus Campeiostachys Drobov according to the International Code of Botanical Nomenclature. Our action is based on the rationale of monophyly, discrimination, and practicality discussed in detail. Currently Elymus contains a vast number of species with different genomes which often, but not always, can be differentiated by cytological and molecular features, but are difficult to separate by traditional morphology, although an effort to do so is detailed and discussed. This difficulty can be attributed to the dominance effect of a particular genome on the other genome(s) present. Campeiostachys, with genome constitution StStHHYY, is a recent addition to a number of genera recently segregated out of Elymus, i.e. Douglasdeweya (StStPP), Kengyilia (StStPPYY), and Roegneria (StStYY, StStStStYY). A key to Campeiostachys taxa is provided, along with taxa descriptions, distribution, nomenclature, and cytology. Nineteen nomenclatural novelties, or combinations, resulted from this work, 10 species names, and nine varietal names.

Key words: Elymus, genome, key to species, morphology.