StH, StStH, and StHH, the St genome being from Pseudoroegneria and the H genome from wild barley (Hordeum). Almost all the species are tetraploids. The only known StStH species is Elymus transhyrcanus, Elymus hoffmannii, and Elymus repens, (there is not unanimous agreement on the genomic constitution of Elymus repens). All three species are native to Asia. The only species known to have the genomic constitution of StHH is the South American species Elymus patagonicus.
Perennial plants usually with 2 or more spikelets per node, sometimes with solitary spikelets. Disarticulation usually below the florets, sometimes in the rachis. Spikelets at the middle of the inflorescence 2-3 times as long as the adjacent internode. Glumes usually lanceolate to ovate-lanceolate, sometimes long and subulate. Paleas tapering to a narrow tip, the keels fintely toothed and straight immediately below the tip.
Elymus, even when restricted to species that contain both the St and H, but no other, genomes, is a large, widespread genus. This makes it hard to identify distinguishing features.
Plants perennial, usually clumped, sometimes rhizomatous. Culms 8-180(220) cm tall, usually upright, sometimes decumbent; lowest internode 1-2 mm thick.
Leaf blades 1-25 mm wide, flat or loosely involute.
Inflorescence spikelike, 3-50 cm long, erect to drooping; rachis usually tough, sometimes brittle, termininating in a spikelet; disarticulation usually below the florets, sometimes initially in the rachis and subsequently below the florets.
Spikelets 1-3(5) per node, tangential when solitary, usually ascending to appressed, sometimes divergent, 8-31 mm long, shortly pedicellate, pedicels 0.3-0.6 mm long.
Glumes unawned or awned, sometimes absent or rudimentary, sometimes subulate, if lanceolate 4-15 mm long excluding the awns, if awned awns to 10 mm long, if subulate (10)20-135 mm long. Lemmas 6-16 mm long, acute, mucronate or with awns to 120 mm long, awns straight to recurved. Paleas straight-sided distally, tapering to a narrow tip, keels densely and relatively finely toothed. Lodicules lobed (sometimes weakly so), ciliate. Anthers 0.7-7 mm long.
120-200 taxa. It is difficult to offer a more precise estimate because of questions concerning species boundaries as well as differing generic interpretations.
Temperate and cool regions of Eurasia and the Americas.
There are a serveral different interpretations of Elymus in current use, with the one adopted here (species having both, but only, the St and H genomes) being the narrowest. Somewhat broader are the treatments in the Flora of China, which excludes the species of Kengyilia are excluded, Elytrigia, and Hystrix but includes those of Roegneria, and the treatment in the Flora of North Americ, which includes the species of Roegneria, the type species of Elytrigia, and the type species of Hystrix but excludes other species of Hystrix and, because none are found in North America, the species of Kengyilia.
There are many species of Elymus for which there is no readily accessible description. Another problem is that its members are all too inclined to hybridize - and the hybrids are often partially fertile. An interesting is what the genomic difference is that results in the species that used to be placed in Sitanion having disarticulating rachises. It would seem that, for some reason, the impact of the H genome is greater in these tetraploids than in other members of the genus.
Grasses of the Soviet Union Tsvelev, N.N. 1976. Zlaki CCCR. [Grasses of the Soviet Union]. Nauka, Leningrad [= St. Petersburg], Russia.
Flora Europaea Melderis, A. 1980. Elymus, p. 192-198 in T.G. Tutin, V.H. Heywood, N.A. Burges, D.M. Moore, D.H. Valentine, S.M. Walters, and D.A. Webb (Eds.), Flora Europaea, vol. 5. Cambridge University Press, Cambridge, England.
Flora of China, vol. 22 Pi, Jia and Shu Cao. 2006. Elymus, pp. 400-429 in Wu, ZY, P.H. Raven and DY Hong (eds). Flora of China, vol. 22. Science Press (Beijing) and Missouri Botanical Garden, St. Louis, Missouri, U.S.A.
Flora of North America, vol. 24. Barkworth, M.E., J.J.N. Campbell, and B. Salomon. 2007. Elymus, pp. 288-343 in M.E. Barkworth, K.M.C. Capels, S. Long. L.K. Anderton, and M. Piep (Eds), Flora of North America, vol. 24. Oxford University Press, New York, United States.