The grass genera of the world
Habit, vegetative morphology. Perennial. The flowering culms leafy. Culms woody and persistent; branched above. Primary branches 1–2, or 3. The branching dendroid. Culm leaf sheaths present; deciduous, or persistent; sometimes leaving a persisten girdle; where recorded, not conspicuously auriculate. Culm leaves with conspicuous blades. Culm leaf blades linear, or lanceolate, or triangular. Culm internodes hollow. Unicaespitose, or pluricaespitose. Rhizomes pachymorph. Plants unarmed. Leaves not basally aggregated; with auricular setae (but small), or without auricular setae. Leaf blades lanceolate (acuminate), or linear-lanceolate; broad to narrow; pseudopetiolate; cross veined, or without cross venation; at least demarcated, disarticulating from the sheaths, or disarticulating from the sheaths to persistent. Contra-ligule present, or absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (with numerous spikelets, by contrast with Yushania); non-digitate; spatheate; a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes paniculate; persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 35–40 mm long; oblong, or linear; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (ciliate at the dilated segment apices); the rachilla extension with incomplete florets. Hairy callus absent.
Glumes two; very unequal to more or less equal; shorter than the adjacent lemmas; pointed; awned (the terminal scaberulous subule to 2.5 mm long); carinate; similar (lanceolate, subule-tipped). Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets 3–7. Lemmas similar in texture to the glumes; not becoming indurated; entire; pointed; awned (acuminate into the subule). Awns 1; median; apical; non-geniculate; much shorter than the body of the lemma (about 2.5 mm long). Lemmas carinate. Palea present; relatively long; not convolute; entire (truncate); awnless, without apical setae; not indurated; 2-keeled. Lodicules present; 3; free; membranous; ciliate; not toothed; heavily vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous; without a conspicuous apical appendage. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; longitudinally grooved. Hilum long-linear. Embryo small; not waisted.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (and an even more conspicuous distinction between the epidermes on either side of the midrib - the one smooth and epapillate, the other with abundant prickles and papillate). Papillae present (on the one side of the blade); intercostal. Intercostal papillae several per cell (mostly one median row of small, circular papillae per long-cell). Long-cells similar in shape costally and intercostally to markedly different in shape costally and intercostally (the costals tending to be smaller and narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present (on one side of the blade only); elongated; clearly two-celled; panicoid-type (more or less, but the apical cells consistently blunt). Stomata absent or very rare (confined to the adaxial surface, where each is associated with a ring of over-arching papillae). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies narrowly saddle shaped, or crescentic. Crown cells absent (but costal and intercostal prickles abundant over the papillate half). Costal short-cells conspicuously in long rows (but the costal short-cells often relatively long, and the files frequently interrupted by prickles). Costal silica bodies saddle shaped (abundant and predominating), or panicoid-type (confined to the vicinity of the midrib); when panicoid type, short dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with arm cells; with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib conspicuous (by virtue of its large bundle and abaxially prominent keel); with one bundle only. The lamina symmetrical on either side of the midrib (in transverse section - despite the epidermal distinction). Bulliforms present in discrete, regular adaxial groups (these large, in the middle of each intercostal zone); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming figures (most bundles with Is or anchors). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Guaduinae. 2 species.
Distribution, phytogeography, ecology. Mexico and Central America.
References, etc. Leaf anatomical: studied by us - O. acuminata (Munro) Calderon & Soderstrom.
Special comments. See Clayton and Renvoize (1986) and Soderstrom and Ellis (1987) for very different generic interpretations of the species in this circle of affinity. There are no available generic descriptions adequate for the present purpose. Illustrations. • O. aztecorum: McClure, New World Bamboos (1973). • O. ramirezii: Ruiz-Sanchez (2012), Acta Bot. mexicana
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’.