The grass genera of the world
Habit, vegetative morphology. Annual. Culms 5–30 cm high; herbaceous. Culm nodes with short bristles below the nodes. Leaves auriculate. Sheath margins joined, or free. Leaf blades narrow; flat; without cross venation. Ligule an unfringed membrane; truncate; 0.2–0.8 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile (each spikelet cluster with the lowest one or two members fertile, the other sterile).
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (in clusters); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; falling entire (i.e., the clusters falling). Spikelets in clusters of 1–2 fertile and 1–3 sterile; not secund; distichous.
Female-fertile spikelets. Spikelets 8–15 mm long; compressed laterally; falling with the glumes (i.e., in the clusters); not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; somewhat spinulose; the rachilla extension with incomplete florets. Callus very short.
Glumes two; relatively large; displaced (side by side away from the rachis); subulate; awned (both awn-like); similar (thinly leathery, linear-subulate, with basal capitate hairs). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1–3; clearly specialised and modified in form (forming a tuft of awns).
Female-fertile florets 1–2 (usually the first two). Lemmas modified into the awn; decidedly firmer than the glumes (cartilaginous to leathery); entire; pointed; awned. Awns 1; median; apical; non-geniculate; much shorter than the body of the lemma; entered by several veins. Lemmas hairy (tuberculate on the back, with capitate hairs on the margins); non-carinate; without a germination flap; 5–7 nerved. Palea present; relatively long; apically notched; with apical setae (apical cusps, about 1 mm long); 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; ciliate; not toothed; not or scarcely vascularized. Stamens 3. Anthers 0.8–1.2 mm long. Ovary apically hairy; with a conspicuous apical appendage (below the styles). Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit somewhat adhering to lemma and/or palea; medium sized (4.5–7.5 mm long); ellipsoid; longitudinally grooved; compressed laterally; with hairs confined to a terminal tuft. Hilum long-linear. Embryo large to small (up to 1/3 the caryopsis length). Endosperm hard; without lipid; containing only simple starch grains. Embryo with an epiblast.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (costal long-cells often short). Mid-intercostal long-cells mostly rectangular; having straight or only gently undulating walls. Microhairs absent. Stomata common; 39–45 microns long. Subsidiaries parallel-sided, or parallel-sided and dome-shaped. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Abundant macrohairs present. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous, or horizontally-elongated smooth, or rounded (few).
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. 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 the furrows); in simple fans. All the vascular bundles accompanied by sclerenchyma (but the smallest with minute strands only). Combined sclerenchyma girders present; forming figures (Is and anchors). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Haplomic genome content Q.
Classification. Watson & Dallwitz (1994): Pooideae; Triticodae; Triticeae. Soreng et al. (2015): Pooideae; Triticodae; Triticeae; Hordeinae. 1 species (H. piliferum).
Distribution, phytogeography, ecology. Southwest Asia.
Xerophytic; species of open habitats. On dry slopes.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia graminis and Puccinia striiformis.
References, etc. Morphological/taxonomic: Löve 1984. Leaf anatomical: Metcalfe 1960, and studied by us.
Illustrations. • H. piliferum: Fl. Iraq, 1968
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: 11th December 2017. delta-intkey.com/grass’.