| # The grass genera of the world |

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

### Malacurus Nevski

~ Leymus

Habit, vegetative morphology. Perennial; caespitose. Culms herbaceous. Leaves auriculate. Leaf blades without cross venation. Ligule an unfringed membrane; truncate; 0.7–8 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (with sterile spikelets at the tip of the rachis).

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the clusters reduced to pairs); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired; not secund.

Female-fertile spikelets. Spikelets 8–16 mm long; not noticeably compressed; disarticulating above the glumes; disarticulating between the florets (the rachilla very fragile). Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus absent.

Glumes two (much reduced); very unequal to more or less equal; joined (those of adjacent spikelets sometimes joined), or free; lateral to the rachis, or displaced (much reduced); hairless; glabrous; pointed; awned (awn-like); similar (subulate-setiform). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets.

Female-fertile florets 2–4. Lemmas not becoming indurated; entire, or incised; awnless, or awned. Awns when present, 1; median; from a sinus, or apical; non-geniculate; much shorter than the body of the lemma (no more than 2 mm long); when present, deciduous. Lemmas hairy (densely lanate); non-carinate; without a germination flap; 7–9 nerved. Palea present; relatively long; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; ciliate; not toothed; not or scarcely vascularized. Stamens 3. Ovary apically hairy. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit adhering to lemma and/or palea; not grooved. Hilum long-linear. Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs absent. Stomata common; 69–75 microns long. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals (clearly sunken). Intercostal short-cells common; intercostal short-cells solitary and paired. Costal silica bodies absent to poorly developed (in the material seen); horizontally-elongated smooth, or rounded, or tall-and-narrow.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs. Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 7. 2n = 42. 6 ploid.

Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 1 species (M. lanatus).

Distribution, phytogeography, ecology. Central Asia.

References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: studied by us.

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’.

Contents