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Published In: Species Plantarum 1: 83. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/28/2009)
Acceptance : Accepted

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86. Elymus L. (wild rye)

Plants perennial, sometimes with rhizomes, forming tufts, small to large clumps, or colonies. Flowering stems erect to less commonly ascending or arched, glabrous. Leaf sheaths glabrous or the lowermost roughened or hairy, sometimes glaucous, the ligule short, membranous, rarely absent. Leaf blades flat or with the margins inrolled, glabrous or roughened to hairy, sometimes with a pair of small auricles at the base. Inflorescences erect or arched to nodding, usually with the base held above the uppermost leaf sheath (except sometimes in E. virginicus), with numerous erect to ascending or spreading spikelets spaced densely or loosely along the axis, the internodes 3–25 mm long in various species. Spikelets single or in clusters of 2(3 or 4) at each node of the inflorescence, all similar in size and appearance, all fertile, linear in outline, with 2–8 florets, disarticulating above the glumes or sometimes also at the spikelet base (disarticulating at the nodes of the inflorescence axis in E. longifolius, the joints shed as a unit with the attached spikelets). Glumes present and similar in size and appearance, less commonly highly reduced and uneven or absent, elliptic‑lanceolate to linear, sometimes thickened and hard at the base, the tip with a long or short awn (except sometimes in E. virginicus), glabrous or roughened to hairy. Lemmas with the tip pointed or awned, rounded on the back, glabrous or roughened to hairy, lacking stiff, spinelike hairs along the keel and the margins. Paleas rounded to bluntly pointed at the tip (except in E. canadensis, with pointed to often cleft tips), as long as or shorter than the body of the lemmas. Fruits 4–6 mm long, linear‑oblong, usually somewhat flattened and grooved, dark brown to reddish brown. About 300 species, nearly worldwide.

The generic taxonomy of Elymus is confusing and controversial. Many of the species with spikelets occurring singly along the axis were placed in Agropyron in the older literature (Steyermark, 1963), but that genus has become restricted to a small group of closely related Old World species (see treatment above). The genera Hystrix Moench and Sitanion Raf. were formerly recognized as distinct, based on minor innovations of spikelet morphology and placement, but generally are now accepted as sections within Elymus (even in the strict sense). On the other hand, the relatively broad circumscription of Elymus accepted here includes several large species groups that have been segregated into such genera as Elytrigia Desv., Leymus Hochst., Pascopyrum Á. Löve, Pseudoregneria (Nevski) Á. Löve, and Thinopyrum Á. Löve, among others. These genera generally are based on cytogenetic analysis of genome types and breeding systems, and some are more easily circumscribed morphologically than others. A number of authors (Estes and Tyrl, 1982; Arnow, 1987) have expressed doubts as to the utility of breaking Elymus apart into these more narrowly defined groups. Recently, Assadi and Runemark (1995) studied chromosomal homology in artificial hybrids of various Old World taxa and concluded that although Agropyron (as treated in the present work) has a genome that is well differentiated from that of Elymus, other groups, including Elytrigia, Pseudoregneria, and Thinopyrum, should continue to be treated as part of a broadly circumscribed Elymus.

Hybridization between Elymus species is relatively common, as well as hybridization between Elymus and related genera, such as Hordeum. However, few such hybrids from Missouri are represented in herbaria. Collectors who find plants with unusual morphology should note other species of Triticeae that may be growing in the vicinity.


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1 Spikelets occurring singly (rarely paired) at the nodes of the inflorescence (2)
+ Spikelets in clusters of mostly 2 (rarely 1, 3, or 4) at each node of the inflorescence (5)
2 (1) Plants without rhizomes, forming tufts; spikelets disarticulating above the glumes and between the florets (3)
+ Plants with long-creeping rhizomes, forming large clumps or colonies; spikelets disarticulating below the glumes, shed as an intact unit; anthers (2–)3–6 mm long (4)
3 (2) Spikelets strongly overlapping on the inflorescence axis; glumes and lemmas sharply pointed or awned at the tip; anthers 1.0–2.0(–2.5) mm long 10 Elymus trachycaulus
+ Spikelets not or only slightly overlapping on the inflorescence axis; glumes and lemmas bluntly pointed to rounded or truncate at the tip, awnless; anthers 2.5–6.0 mm long 3 Elymus elongatus subsp. ponticus
4 (2) Leaf blades rarely glaucous, dark green to somewhat bluish green, soft and fairly flexible, the margins flat, the upper surface similar to the lower surface, the fine veins not strongly ridged; glumes elliptic-lanceolate, relatively thin and flexible 7 Elymus repens
+ Leaf blades strongly glaucous, bluish green and silvery, stiff, the margins usually inrolled, the upper surface strongly corrugated (appearing to have 7–14 grooves between the ridged veins); glumes linear, noticeably thickened and firm 9 Elymus smithii
5 (1) Inflorescences disarticulating at the nodes at maturity, the joints shed as a unit with the attached spikelets; glumes (including the long awn) 40–110 mm long 6 Elymus longifolius
+ Inflorescences with the axis persistent, not breaking into segments at maturity, the spikelets disarticulating above the glumes or sometimes also at the spikelet base; glumes (including the awn) 11–40 mm long or sometimes lacking (6)
6 (5) Glumes absent, or if present then either both glumes less than 3 mm long or the upper glume much longer than the lower glume (more than 5 mm difference in length) (7)
+ Glumes always present, 10–40 mm long (including the awn in awned species), equal in length or nearly so (less than 5 mm difference in length) (8)
7 (6) Spikelets erect or strongly ascending; lemmas hairy, with at least some of the awns noticeably bent or arched outward 2 Elymus diversiglumis
+ Spikelets spreading at a right angle to the inflorescence axis at maturity; lemmas glabrous or roughened, with the awns all straight or very slightly curved 5 Elymus hystrix
8 (6) Spikelets with all or most of the awns noticeably bent or arched outward at maturity; paleas mostly 8.5–12.5 mm long 1 Elymus canadensis L. var. canadensis
+ Spikelets with the awns straight or slightly curved, but not bent or arched outward (rarely awnless or nearly so in E. virginicus); paleas mostly 5.5–8.5 mm long (9)
9 (8) Glumes relatively soft, thin, and flat at the base, 3- or 5-nerved throughout 4 Elymus glaucus Buckley subsp. glaucus
+ Glumes thickened and hardened at the base, 3- or 5-nerved only above the thickened area (10)
10 (9) Inflorescences erect or nearly so; glumes 0.8–2.5 mm wide, expanded and flattened above the bowed-out base, remaining attached to the lowermost floret at disarticulation, leaving a naked inflorescence axis 12 Elymus virginicus
+ Inflorescences usually curved or nodding at maturity; glumes 0.2–1.0 mm wide, not or only slightly expanded above the relatively straight base, persistent on the inflorescence axis and not shed with the florets (11)
11 (10) Leaf blades glabrous or roughened, often glaucous, pale green to green and not shiny; spikelets mostly with 2–4 florets; paleas mostly 7–8 mm long 8 Elymus riparius
+ Leaf blades usually hairy on the upper surface, not glaucous, dark green and somewhat shiny; spikelets with 1 or 2 florets; paleas mostly 5.5–7.0 mm long 11 Elymus villosus
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