The grass genera of the world
Habit, vegetative morphology. Annual; caespitose. Culms 7–30 cm high; herbaceous; unbranched above. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; about 0.8–1.6 mm wide; almost filiform; rolled (involute); without cross venation; persistent. Ligule an unfringed membrane; not truncate (acuminate, becoming lacerate); 1.5–4 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single spike (slender), or a single raceme (with short pedicels), or paniculate (rarely, having two spikelets per node, on different pedicels or on one branched peduncle); contracted; spicate. Rachides hollowed. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary (mostly), or paired (occasionally); not secund; distichous; subsessile to pedicellate (the pedicels embedded with the spikelets the rachis hollows, becoming shorter towards the inflorescence tip); imbricate.
Female-fertile spikelets. Spikelets 4–7 mm long; compressed laterally (flatwise against the axis); disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension naked. Hairy callus present. Callus short (oblique).
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (exceeding them); free; lateral to the rachis; hairless; glabrous (minutely scabrous on the nerves); pointed; awnless; non-carinate (but keeled on the outer nerves); similar (usually purplish-tinged, both strongly keeled on the outer nerve with the side adjoining the rachis nerveless, one - assumed to be the G1 - markedly narrower). Lower glume two-keeled (G2 also); 2 nerved. Upper glume 4 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 1. Lemmas less firm than the glumes (membranous); not becoming indurated; incised; 2 lobed; not deeply cleft (shortly bifid); awned. Awns 1; median; from a sinus; non-geniculate; hairless; much shorter than the body of the lemma to much longer than the body of the lemma; entered by one vein. Lemmas hairless; glabrous; carinate; without a germination flap; 3–5 nerved. Palea present; relatively long; tightly clasped by the lemma; briefly apically notched; awnless, without apical setae; thinner than the lemma (hyaline, glabrous); not indurated; 2-nerved; keel-less (the nerves closely apposed). Lodicules present; 2; free; membranous; glabrous; not toothed; not or scarcely vascularized. Stamens 1. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2.5 mm long); fusiform; not noticeably compressed. Hilum short (punctiform). Embryo small (but fairly large for a pooid grass - about 1/4 of the grain length). Endosperm hard; with lipid; containing compound starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs absent. Stomata common; (31–)34–38(–39) microns long. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals (slightly). Intercostal short-cells absent or very rare. Costal short-cells predominantly paired. Costal silica bodies absent (in material seen), or present and well developed; when present, horizontally-elongated smooth, or rounded.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade with slight, rounded adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous (by its association with a small abaxial keel, and by the bundle possessing an abaxial strand rather than a girder); 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 (all the main bundles with Is). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 13.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Holcinae. 1 species (S. bolanderi).
Distribution, phytogeography, ecology. Western U.S.A.
Rusts and smuts. Rusts Puccinia.
References, etc. Leaf anatomical: studied by us.
Illustrations. • S. bolanderi: Hitchcock and Chase (1950)
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’.