Family: Poaceae |
Mary E. Barkworth Plants perennial; sometimes cespitose, often rhizomatous. Culms 10–350 cm, erect, with extravaginal branching. Leaves basal or evenly distributed; sheaths open; auricles usually present; ligules membranous, truncate to rounded; blades often stiff, adaxial surfaces usually with subequal, closely spaced, prominently ribbed veins, sometimes with unequal, widely spaced, not prominently ribbed veins. Inflorescences usually distichous spikes with 1–8 spikelets per node, sometimes panicles with (2)3–35 spikelets associated with each rachis node; rachises with scabrous or ciliate edges; internodes3.5–12(15) mm. Spikelets 1/2–3 3/4 times the length of the rachis internodes, usually sessile, sometimes pedicellate, pedicels to 5 mm, appressed to ascending, with 2–12 florets, the terminal floret usually reduced; disarticulation above the glumes, beneath the florets. Glumes usually 2, usually equal to subequal, the lower or both glumes sometimes reduced or absent, lanceolate and narrowing in the distal 1/4, or lanceolate to subulate and tapering from below midlength, pilose or glabrous, sometimes scabrous, 0–3(7)-veined, veins evident at least at midlength, sometimes keeled, keels straight or almost so, apices acute, acuminate, or tapering to an awnlike tip, if distinctly awned, awns to 4 mm; lemmas glabrous or with hairs, sometimes scabrous distally, inconspicuously 5–7-veined, rounded over the back proximally, sometimes keeled distally, keels not conspicuously scabrous distally, apices acute, unawned or awned, awns usually to 7 mm, sometimes 16–33 mm, straight; paleas slightly shorter than to slightly longer than the lemmas, keels usually scabrous or ciliate on the distal portion, sometimes throughout; lodicules 2, shortly hairy, lobed; anthers 3, 2.5–10 mm. Caryopses with hairy apices. x = 7. Haplomes Ns, Ns or Xm. Name an anagram of Elymus. Yen et al. (2009) presented a synopsis of Leymus in which they recognized 61 species. All the species are native to temperate regions in the Northern Hemisphere, the greatest diversity being present in eastern Asia, with North America being a secondary center. They recognized three sections in the genus. Sect. Leymus has long, relatively thick rhizomes and lanceolate lemmas. Its members grow in open, sunny areas on the shores of seas, lakes, and rivers and in sand dunes. Species of Sect. Anisopyrum may lack rhizomes but, in those that have them, the rhizomes are thinner. The species also differ from those of sect. Leymus in having subulate glumes and, in a few instances, highly reduced glumes. Like the species of sect. Leymus, members of sect. Anisopyrum grow in open, sunny locations but in steppe and meadow environments rather than bodies of water pr and dunes. Sect. Silvicola includes most of the species that used to be placed in Hystrix, but not the type species of that genus, Elymus hystrix. They differ from members of the other two sections in having no or only vestigial glumes and in growing in shady, forested areas. They also differ in growing in prefering more acidic soils than members of the other sections. Phylogenetic analysis by Sha et al. (2008) is not strongly supportive of this sectional treatment. Whether this reflects their reliance on the ITS region, inadequate sampling, or the polyphyletic origin of the characters used to delimit the sections is not clear. Members of sects. Leymus and Anispyrum are used for soil stabilization and forage. All the species are self-incompatible, outcrossing polyploids. One of the haplomes present is the Ns genome; this genome is also found in Psathyrostachys, most species of which are diploids. There is disagreement concerning the second haplome. Wang and Jensen (1994) argued there are two different haplomes present, the origin of the second one being unknown and designated Xm. Bödvarsdóttir and Anamthawat-Jónsson (2003; Anamthawat-Jónsson 2005) found no molecular probes that would distinguish between the two genera, from which they argued that Leymus is a segmental allopolyploid with only one basic haplome, Ns. Morphologically, Psathyrostachys and Leymus, are very similar, the major differences being that Psathyrostachys is never rhizomatous, has disarticulating rachises, and, usually, distinctly awned lemmas. Of the 17 species treated here, 11 are native to the Flora region, 5 are introduced, and 2 are naturally occurring hybrids. Leymus arenarius and L. mollis are sometimes mistaken for Ammophila, which grows in the same habitats and has a similar habit. Ammophila differs from Leymus, however, in having only one floret per spikelet. In most species of Leymus, at least some of the spikelets are on pedicels up to 2 mm long. Despite this, it is customary to identify the inflorescence of such species as a spike rather than a raceme, as is done in this treatment. Culm thicknesses are measured on the lower internodes. Descriptions of rachis nodes, unless stated otherwise, apply to the internodes at midspike. The following papers relate to the taxonomy of Leymus. In most cases, all that is provided are links to other sites. They are grouped by subject. HORDELYMUS: Cytogenetic and some molecular data show that Hordelymus has the Ns genome but Dizkirici et al., who examined ITS data, found that it was distantly related to the other Ns species that they examined. Dizkirici et al. 2011. Phylogenetic relationships of Elymus L. and related genera (Poaceae) based on the nuclear ribosomal internal transcribed spacer sequences Turk J Bot 34 (2010) 467-478; doi:10.3906/bot-0912-249. Ellneskog-Staam et al. 2006. Identifying the genome of wood barley Hordelymus europaeus (Poaceae: Triticeae. Hereditas 143: 103-112. Ni, Y. et al. 2011. Maternal origin, genome constitution and evolutionary relationships of polyploid Elymus species and Hordelymus europaeus. Biologia Plantarum 55: 68-74. doi 10.1007/s10535-011-0009-7. HYSTRIX: Several (but not all) species that used to be included in Hystrix have been transferred to Leymus based on cytological and molecular information. Ellneskog-Staam et al. 2007. Genome analysis of species in the genus Hystrix (Triticeae; Poaceae.)Pl. Syst. Evol. 265: 241–249 (2007)DOI 10.1007/s00606-006-0509-7 Zhang HQ, Fan X, Sha LN, Zhang C, Yang RW, Zhou YH. 2008. Phylogeny of Hystrix and related genea (Poaceae: Triticeae) based on nuclear rDNA ITS sequences. Plant Biol. (Stuttg.) 10:635-42. doi: 10.111/j.1438-8677.2008.00065.x. |