Leymus Hochst. (Gramineae: Triticeae) in North America: Taxonomy and Distribution

Leymus Hochst., a segregate genus of Triticeae, can be recognized morphologically and genomically. Its members exhibit all or all but one of the following morphological characterstics: rhizomatous habit; unawned, short, often stiffly subulate, glumes that tend to lie opposite the sides rather than the midveins of the lemmas; unawned, or only shortly awned, lemmas; and long anthers. They are all polyploids based on the same pair of genomes, one from Psathyrostachys and the other from Thinopyrum. Fourteen species occur in North America, including two interspecific hybrids. One new subspecies is described, L. salinus subsp. mojavensis. A key, descriptions, and distribution maps are given. In addition, one new hybrid genus, × Leytesion, and several new combinations are published to accommodate the naturally occurring intergeneric hybrids involving Leymus.