Family: Poaceae |
Mary E. Barkworth, Julian J.N. Campbell and Bjorn Salomon Plants perennial; sometimes cespitose, with or without rhizomes, sometimes stoloniferous. Culms 8–180(220) cm, usually erect to ascending, sometimes strongly decumbent to prostrate, usually glabrous. Leaves usually evenly distributed, sometimes somewhat basally concentrated; sheaths open for most of their length; auricles often present; ligulesmembranous, truncate or rounded, sometimes acute, entire or erose, often ciliolate; blades 1–24(25) mm wide, abaxial surfaces usually smooth or scabrous, sometimes with hairs, adaxial surfaces scabrous or with hairs, particularly over the veins, usually with unequal, not strongly ribbed, widely spaced veins, sometimes with equal, strongly ribbed, closely spaced veins. Inflorescences spikes, usually exserted, with 1–3(5) spikelets per node, internodes (1.5)2–26 mm; rachises with scabridulous, scabrous, or ciliate edges. Spikeletsusually appressed to ascending, sometimes strongly divergent or patent, with 1–11 florets, the distal florets often reduced, the lowest florets usually functional, sterile and glumelike in some species; disarticulation usually above the glumes and beneath each floret, sometimes also below the glumes or in the rachises. Glumes usually 2, absent or highly reduced in some species, usually equal to subequal, sometimes unequal, usually linear-lanceolate to linear, setaceous, or subulate, sometimes oblanceolate to obovate, (0)1–7-veined, sometimes keeled over 1 vein, not necessarily the central vein, the keel vein sometimes extended into an awn; lemmas linear-lanceolate, obscurely 5(7)-veined, apices acute, often awned, sometimes bidentate, teeth to 0.2 mm, sometimes with bristles, bristles to 10 mm, awns terminal or from the sinus, straight or arcuately divergent, not geniculate; paleas from shorter than to slightly longer than the lemmas, keels scabrous or ciliate, at least in part; anthers 3, 0.7–7 mm. Caryopses with hairy apices. x = 7. Haplomes St, H, Y, P. Name from the Greek elyo, ‘rolled up’, the caryopses being tightly embraced by the lemma and palea. As interpreted here, Elymus is a widespread, north-temperate genus of about 150 species. It includes Sitanion Raf. and Roegneria K. Koch, but moves some taxa that others include in Elymus to Leymus , Pascopyrum , Pseudoroegneria, and Thinopyrum. [Recently (Barkworth 2009), I agreed with Yen et al. in adopting a narrower interpretation of the genus. That would move Elymus ciliaris to Roegneria ciliaris and and , in which Roegneriaand Thirty-two species of Elymus are native to the Flora region. Of the seven non-native species treated, one is established (E. repens ), two are distributed as forage (E. dahuricus and E. hoffmannii ), two are known from ballast dumps and are not established (E. tsukushiensis and E. ciliaris), and two (E. caninus and E. semicostatus ) have been attributed to the Flora region but specimens documenting the reports have not been located. Eight named, naturally occurring, intrageneric hybrids are described at the end of the treatment. They are not included in the key. As mentioned in the descriptions of the non-hybrid species, other interspecific hybrids undoubtedly exist. Because many of the hybrids are partially fertile, backcrossing and introgression occurs. Intergeneric hybrids are treated under ×Elyhordeum, ×Elyleymus , ×Pascoleymus, ×Pseudelymus , and ×Triticosecale; most are sterile. The complex patterns of morphological diversity within Elymus in North America probably reflect a combination of multiple origins involving different progenitors, introgression, hybridization both within the genus and with other members of the tribe, and morphological plasticity. Little is known concerning the relative importance of these factors. Two infraspecific ranks have been used to aid in circumscribing the known variation. In general, infraspecies taxa that show great morphological and ecological distinction are treated as subspecies; others, as varieties. All species of Elymus are alloploids that combine one copy of the St haplome present in Pseudoroegneria with at least one other haplome. So far as is known, all species that are native to North America, as well as many species native to northern Eurasia, are tetraploids with one additional haplome, the H genome from Hordeum sect. Critesion . Many Asian species combine the St haplome with the Y haplome, for which there are no known diploids; such species are sometimes placed in the segregate genus Roegneria. This treatment includes two such species, E. ciliaris and E.semicostatus. In addition, the treatment includes two hexaploid species, E. tsukushiensis and E. dahuricus, that combines all three haplomes. Elymus repens and E. hoffmannii, the other two hexaploid species in this treatment, basically combine two copies of the St haplome with one of the H haplome, but the molecular data for E. repens point to a more complex situation (Mason-Gamer 2001). For further discussion of generic delimitation in the Triticeae, see Barkworth (2000), Yen et al. (2005), and Barkworth and von Bothmer (2005). Elymus is sometimes divided into multiple sections (see, for example, Tsvelev 1976; Löve 1984). There are, however, no detailed morphological descriptions of the sections, making it difficult to determine how to treat the North American species. It is notable that the species with solitary spikelets are concentrated in western and northern North America, whereas the species with multiple spikelets at a node are most prevalent east of the Rocky Mountains, from southern Canada to the Gulf Coast. There are exceptions to this statement. For instance, species with multiple spikelets and disarticulating rachises are primarily western in their distribution, and E. glaucus , a species with multiple spikelets and non-disarticulating rachises, is western. Like the western species with solitary spikelets, and unlike most eastern species, its glumes have a hyaline margin. In the key and descriptions, unless otherwise stated, the following conventions are observed: the number of culm nodes refers to the number of nodes above the base; measurements of spikes include the awns, while measurements of spikelets, glumes, and lemmas do not; rachis internodes are measured in the middle of the spike; glume widths of lanceolate to linear glumes are measured at the widest point, and those of linear to setaceous glumes about 5 mm above the base of the glumes; the number of florets in a spikelet includes the distal reduced, sterile florets; and dates of anthesis, when provided, are for the central range of each species. The curvature of the lemma awns is often important in identifying individual species. The curvature increases with maturity, and may vary within a spike. If a plant appears to have at least some strongly curved lemma awns, it should be taken through the “strongly curved” side of the key. SELECTED REFERENCES Barkworth, M.E. 1997. 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