| # The grass genera of the world |

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

### Leymus Hochst.

Including Aneurolepidium Nevski

Excluding Malacurus

Habit, vegetative morphology. Perennial; rhizomatous (or turf-forming). Culms 20–150 cm high; herbaceous; branched above, or unbranched above (commonly). The branching simple, or fastigiate (rarely, e.g. L. ramosus). Culm internodes hollow. Young shoots extravaginal. Leaves mostly basal (often), or not basally aggregated; auriculate (the auricles lanceolate-crescentic), or non-auriculate. Sheath margins free. Leaf blades linear (harsh, glaucus, pungent); broad, or narrow; 2–15 mm wide; flat, or rolled (convolute); not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule an unfringed membrane; truncate, or not truncate; 0.2–1(–3) mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; outbreeding.

Inflorescence. Inflorescence a single spike, or a false spike, with spikelets on contracted axes (erect, linear, rarely oblongate); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired to in triplets (rarely solitary or in clusters of up to six); not secund; distichous; subsessile; usually imbricate.

Female-fertile spikelets. Spikelets (6–)8–20(–25) mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes; disarticulating between the florets (the joints well developed). Rachilla prolonged beyond the uppermost female-fertile floret; hairy (shortly pilose), or hairless (scabrous); the rachilla extension with incomplete florets. Hairy callus present, or absent. Callus blunt (triangular or rounded).

Glumes two; very unequal to more or less equal; shorter than the adjacent lemmas to long relative to the adjacent lemmas; joined (basally), or free; when scoreable, lateral to the rachis, or displaced (side by side); hairy (short pilose), or hairless (scabrous or rarely glabrous); when hairless glabrous (rarely), or scabrous; pointed (linear lanceolate to almost setiform); subulate, or not subulate; awned to awnless; carinate (often), or non-carinate; similar. Lower glume 1–3 nerved. Upper glume 1–3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.

Female-fertile florets (2–)3–7(–12). Lemmas acute, with a cusp or awn; similar in texture to the glumes (leathery); not becoming indurated; entire; pointed; mucronate, or awned. Awns when present, 1; median; apical; non-geniculate; much shorter than the body of the lemma (up to 4 mm long); entered by several veins. Lemmas hairy (pilose), or hairless; when hairless glabrous, or scabrous; non-carinate; without a germination flap; 5 nerved, or 7 nerved; with the nerves confluent towards the tip. Palea present; relatively long (almost equalling the lemma); awnless, without apical setae; not indurated; 2-nerved; 2-keeled (pilose or scabrous along the keels, and often between them). Lodicules present; 2; free; membranous; ciliate; not toothed (usually entire). Stamens 3. Anthers 5–7 mm long (relatively long); not penicillate; without an apically prolonged connective. Ovary apically hairy; without a conspicuous apical appendage. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea; small to medium sized (2.5–9 mm long); longitudinally grooved; compressed dorsiventrally; usually with hairs confined to a terminal tuft. Hilum long-linear. Embryo small. Endosperm hard; without lipid; containing only simple starch grains. Embryo without an epiblast; without a scutellar tail; with a negligible mesocotyl internode; with one scutellum bundle. Embryonic leaf margins meeting.

First seedling leaf with a well-developed lamina. The lamina narrow.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or lacking. Papillae absent. Long-cells of similar wall thickness costally and intercostally, or differing markedly in wall thickness costally and intercostally. Mid-intercostal long-cells having markedly sinuous walls. Microhairs absent. Stomata common. Subsidiaries dome-shaped. Intercostal short-cells common; in cork/silica-cell pairs (and solitary); silicified. Costal short-cells predominantly paired (and solitary). Costal silica bodies rounded, or tall-and-narrow (or more or less rectangular); not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size (e.g., L. condensatus), or with the ribs very irregular in sizes (e.g. L. arenarius). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (in the furrows, often small and variable in size, cf. Ammophila); sometimes in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 7. 2n = 28, 42, 56, and 84. 4, 6, 8, and 12 ploid. Haplomic genome content J and N. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. About 30 species.

Distribution, phytogeography, ecology. In the non-tropical southern hemisphere and especially mountains of central Asia and North America.

Commonly adventive. Mesophytic, or xerophytic (often littoral or halophytic); species of open habitats; halophytic, or glycophytic. With a wide habitat range, including coastal sand dunes.

Economic aspects. Including useful sandbinders.

Hybrids. Intergeneric hybrids with Agropyron (×Leymopyron Tsvelev), Elytrigia (×Leymotrigia Tsvelev), Psathyrostachys (×Leymostachys Tsvelev), Thinopyrum (several species involved). See also ×Elyleymus Baum.

Rusts and smuts. Rusts — Puccinia.

References, etc. Morphological/taxonomic: Löve 1984; Atkins, Barkworth and Dewey 1984. Leaf anatomical: Metcalfe 1960 (after nomenclatural adjustments); studied by us - L. arenarius (L.) Hochst.

Illustrations. • Leymus arenarius (as Elymus): © C.E. Hubbard (1968). • Leymus racemosus, as Elymus giganteus: P. Beauv. (1812). • Leymus arenarius (as Elymus), general aspect: Eng. Bot. (1872). • Grass pollen antigens: Watson and Knox (1976).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 15th June 2025. delta-intkey.com’.

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