The grass genera of the world
Including Greenia Nutt, Sclerachne Trin., Thurberia Benth.
Habit, vegetative morphology. Annual; caespitose. Culms 20–50 cm high; herbaceous; branching basally. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; flat (pubescent); not pseudopetiolate; without cross venation. Ligule an unfringed membrane; not truncate (lacerate); 1–2 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (narrow); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 3–4 mm long; not noticeably compressed; falling with the glumes. Rachilla prolonged beyond the uppermost female-fertile floret (as a short bristle); the rachilla extension naked. Hairy callus absent. Callus conspicuous, beneath the glumes.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; often densely hairy (hispidulous or pilose); pointed (acute); awnless; non-carinate; similar (firm, leathery). Lower glume 3 nerved. Upper glume 3 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 (bidentate); awned. Awns 1; median; dorsal; from near the top; geniculate; hairless; much longer than the body of the lemma (slender, 8–10 mm long); entered by one vein. Lemmas hairless; weakly carinate, or non-carinate; without a germination flap; inconspicuously 3 nerved. Palea present; conspicuous but relatively short; thinner than the lemma (hyaline); 2-nerved; keel-less. Lodicules present; 2; free; membranous; glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small (2.5 mm long). Embryo small. Endosperm hard; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally; of similar wall thickness costally and intercostally, or differing markedly in wall thickness costally and intercostally. Mid-intercostal long-cells rectangular and fusiform (mostly); having straight or only gently undulating walls. Microhairs absent. Stomata common (adjoining the veins). Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies horizontally-elongated crenate/sinuous (with a few deeply crenate examples approaching nodular); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with the ribs more or less constant in size. Midrib with one bundle only. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid. Nucleoli disappearing before metaphase.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Agrostidinae. 1 species (L. arkansana).
Distribution, phytogeography, ecology. Southern U.S.A..
Xerophytic; species of open habitats. Prairie.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia graminis.
References, etc. Leaf anatomical: studied by us.
Illustrations. • L. arkansana: 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’.