Historical and Current Taxonomic Perspectives of Agropyron, Elymus, and Related Genera1

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Abstract
The taxonomy of the perennial grasses of the Triticeae tribe (Agropyron, Elymus, et al.) has been in an unsettled state for many years, with Eurasian and North American authorities often using different systems of classification and applying different names to the same species. North Americans have generally relied on the treatment given in A.S. Hitchcock's 1951 Manual of the Grasses of the United States, while realizing that it was seriously outdated. Publication of treatments of the Triticeae in Poaceae URSS by N.N. Tzvelev in 1976 and in Flora Europaea by A. Melderis et al. in 1980 has made it advisable for North Americans to reevaluate their taxonomic traditions with respect to these grasses. Tzvelev's treatment is compatible with biological relationships as determined by chromosome pairing in interspecific and intergeneric hybrids. The perennial genera of the Triticeae recognized by Tzvelev include: 1) Agropyron (restricted to A. cristatum and other crested wheatgrasses), 2) Elymus (self‐fertilizing and caespitose species previously in Elymus and Agropyron) 3) Leymus (usually cross‐pollinating and often rhizomatous species previously in Elymus), 4) Elytrigia (usually cross‐pollinating and rhizomatous or caespitose species previously included in Agropyron, with the exception of the crested wheatgrasses), 5) Psathyrostachys (crosspollinating species with brittle rachises and multiple spikelets, including Russian wildrye), and 6) Hordeum (treated in its traditional sense). With a few exceptions, I endorse Tzvelev's treatment because it closely reflects biological and phylogenetic relationships.