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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Duthiea Hackel

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 T’s 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)


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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’.

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