Leymus, commonly called wild ryes, is a genus of approximately 30–60 perennial grasses in the family Poaceae (order Poales), widespread across the temperate and cold regions of the Northern Hemisphere, including Europe, Asia, and the Americas.
Plants in this genus are perennial, sometimes growing in tufts (cespitose) but more characteristically spreading by elongate rhizomes. Culms (stems) range from 10 to 350 cm tall and grow erect with extravaginal branching. Leaves may be basal or distributed along the stem; sheaths are open and auricles are usually present. The leaf blades are often stiff with prominently ribbed veins on the adaxial (upper) surface. Ligules are membranous and truncate to rounded.
The inflorescence is typically a distichous spike bearing 1–8 spikelets at each node, though some species form panicles. Spikelets are usually sessile, each containing 2–12 florets; disarticulation occurs above the glumes. Lemmas are inconspicuously 5–7-veined, typically unawned or with short awns (usually to 7 mm, occasionally to 33 mm). The base chromosome number is x = 7.
Leymus is closely related to Elymus and was segregated from it — the genus name is an anagram of Elymus. Notable members include Leymus cinereus (basin wild rye) of western North America, Leymus arenarius (lyme grass) of Europe, Leymus chinensis of East Asia, and Leymus racemosus (mammoth wild rye) of Eurasia. Several species are valued for erosion control, forage, and habitat restoration.
Etymology
The name Leymus is an anagram of Elymus, the closely related genus from which it was segregated. This naming reflects the two genera's morphological similarity while marking their distinctness; Leymus differs from Elymus primarily in being outcrossing and typically having longer anthers and shorter awns.
Distribution
Leymus is distributed across the temperate and cold-temperate regions of the Northern Hemisphere, with species native to Europe (including L. arenarius along Atlantic and Baltic coasts), Central Asia, Siberia, East Asia (China, Mongolia, Korea, Japan), and the Americas from Alaska and Canada south through the western United States into Baja California and northern Mexico. A few species extend into South America (Chile, Argentina). The genus includes arctic-adapted species as well as plants of inland steppes, dunes, and riparian zones.
Ecology
Most Leymus species inhabit open, often dry or seasonally dry environments — steppes, prairies, dunes, river banks, and disturbed ground. Many species spread aggressively by rhizomes, which helps them stabilize sandy or loose soils and colonise disturbed sites. Their stiff, ribbed leaf blades and tolerance of drought and salinity make them characteristic grasses of continental interiors and coastal dunes. Leymus cinereus (basin wild rye) is prominent in sagebrush shrublands of western North America; L. arenarius is a major dune-stabilizing grass in northern Europe.
