The grass genera of the world
Including Thrixgyne Keng, Triavenopsis Candargy
Habit, vegetative morphology. Perennial; rhizomatous, or caespitose. Culms 20–70 cm high; herbaceous; unbranched above. Young shoots intravaginal. Leaves not basally aggregated (often overtopping the inflorescence); non-auriculate. Leaf blades linear; narrow; 2–6 mm wide; flat, or rolled (usually convolute); not pseudopetiolate; without cross venation. Ligule an unfringed membrane; not truncate; 5–8 mm long (lacerate).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence few spikeleted, or many spikeleted; a single raceme, or paniculate (the lower nodes with well developed collars); contracted (the spikelets often gathered into a short unilateral cluster); spatheate (the lowest spikelet and sometimes some others subtended by a deciduous, membranous scale of unknown homology); not comprising partial inflorescences and foliar organs. Spikelets secund (the raceme unilateral), or not secund; pedicellate.
Female-fertile spikelets. Spikelets 15–25 mm long; compressed laterally to not noticeably compressed; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy, or hairless; the rachilla extension with incomplete florets, or naked. Hairy callus present.
Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; pointed (acute to acuminate); slightly awned to awnless; non-carinate; similar (membranous with thinner margins). Lower glume 5–9 nerved. Upper glume 7–13 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets when present, distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets (1–)2–3(–9). Lemmas ovate; similar in texture to the glumes to decidedly firmer than the glumes (herbaceous to leathery, with thin margins and tip); incised; 2 lobed; deeply cleft to not deeply cleft (from bidentate to cleft to a third or more); awned. Awns 1; median; from a sinus; geniculate; much longer than the body of the lemma; entered by one vein. Lemmas hairy. The hairs in tufts; in transverse rows (the tufts in a median horizontal row). Lemmas non-carinate; without a germination flap; 9–13 nerved. Palea present; relatively long; apically notched; awnless, without apical setae, or with apical setae to awned (sometimes 2-aristulate); 2-nerved; 2-keeled. Palea keels wingless. Lodicules absent. Stamens 3. Anthers penicillate. Ovary apically hairy. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit beaked via the persistent style; hairy on the body. Hilum long-linear. Embryo small.
Abaxial leaf blade epidermis. Costal/intercostal zonation fairly conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (the costals smaller); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (and pitted). Microhairs present (possibly - one doubtful example seen), or absent (?). Stomata absent or very rare. Intercostal short-cells absent or very rare. Costal prickles present. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies few (though abundant adaxially); panicoid-type; more or less nodular.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib seemingly not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (at bases of furrows); in simple fans (these small). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (the large bundles with Ts and anchors). Sclerenchyma not all bundle-associated. The extra sclerenchyma in abaxial groups (of 1–3 cells); abaxial-hypodermal, the groups isolated (opposite the furrows).
Special diagnostic feature. Plant and inflorescence not as in Lygeum (q.v.).
Cytology. Chromosome base number, x = 7. Haploid nuclear DNA content unknown, but the chromosomes large.
Classification. Watson & Dallwitz (1994): Pooideae, or Arundinoideae; if pooid, Poodae; Aveneae (?); if arundinoid, Danthonieae (?). Soreng et al. (2015): Pooideae; Phaenospermateae. 3 species.
Distribution, phytogeography, ecology. Himalayas.
Species of open habitats. Mountain slopes.
References, etc. Leaf anatomical: this project.
Illustrations. • D. bromoides: Hook. Ic. Pl. 25 (1886)
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’.