The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose (from short rhizomes). The flowering culms leafy. Culms 30–50 cm high; herbaceous; unbranched above. Plants unarmed. Leaves not basally aggregated; without auricular setae. Leaf blades broad; 1–2.5 mm wide; pseudopetiolate; cross veined; rolled in bud. Contra-ligule absent.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic (male spikelets mostly shorter pedicelled, reduced). Plants with inflorescences hardly exserted from the sheaths, inconspicuous.
Inflorescence. Inflorescence determinate, or indeterminate (most species with synflorescences); paniculate (often depauperate, having axillary partial inflorescences or synflorescences of variously reduced panicles). Spikelet-bearing axes paniculate; persistent. Spikelets not secund; pedicellate (the female pedicels thickened apically); consistently in long-and-short combinations, or not in distinct long-and-short combinations.
Female-sterile spikelets. Male spikelets reduced to lemma, palea and 2–3 free, non-penicillate stamens; sometimes awned. Rachilla of male spikelets terminated by a male floret. The male spikelets without glumes; without proximal incomplete florets; 1 floreted. The lemmas awnless, or awned. Male florets 1; 2 staminate, or 3 staminate. The staminal filaments free.
Female-fertile spikelets. Spikelets 9–20 mm long; compressed dorsiventrally (not gibbous); disarticulating above the glumes; with a distinctly elongated rachilla internode above the glumes. Rachilla terminated by a female-fertile floret. Callus short (columnar).
Glumes two; more or less equal; long relative to the adjacent lemmas; hairless; awnless (sometimes acuminate); non-carinate; similar (thin, firm). Lower glume 5 nerved. Upper glume 5 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (bony); becoming indurated; entire; pointed; awnless, or mucronate (?); hairy, or hairless; non-carinate; having the margins inrolled against the palea; 5 nerved. Palea present (enclosed by lemma margins); relatively long; entire; awnless, without apical setae; indurated; 2-nerved. Lodicules present; 3; free; fleshy; glabrous; heavily vascularized. Stamens 0. Ovary apically glabrous. Styles fused (into one long style). Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; compressed dorsiventrally. Hilum long-linear. Embryo small.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (on the interstomatal cells, and also on the subsidiaries). Intercostal papillae over-arching the stomata; several per cell (mostly around the edges of the interstomatals, and concentrated around the stomata). Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (fairly thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries papillate; triangular. Intercostal short-cells common; in cork/silica-cell pairs (and solitary). Costal short-cells conspicuously in long rows. Costal silica bodies saddle shaped, or oryzoid (at least, some approaching this), or panicoid-type; when panicoid type, fat cross shaped.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; with adaxial palisade (of large arm cells); with arm cells (these conspicuous); with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups large). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the main bundles); forming figures (most bundles with an anchor). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10 and 11. 2n = 20 and 22. 2 ploid.
Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Olyreae. Soreng et al. (2015): Bambusoideae; Bambusodae; Olyreae; Olyrinae. 5 species.
Distribution, phytogeography, ecology. Central and South America.
References, etc. Morphological/taxonomic: Soderstrom 1982a and 1982b; Soderstrom and Zuloaga 1988. Leaf anatomical: this project.
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: 13th November 2017. delta-intkey.com/grass’.