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The grass genera of the world

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

Tridentopsis P.M. Peterson

~ = Tricuspis mutica Torr.

Type species: T. mutica (Torr.) P.M. Peterson.

Habit, vegetative morphology. Perennial. Culms 20–100 cm high. Leaves without auricular setae. Leaf blades flexible, not sharp-tipped, not needle-like; not pseudopetiolate. Ligule present; an unfringed membrane, or a fringed membrane.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence paniculate; open, or contracted. Spikelets solitary; pedicellate.

Female-fertile spikelets. Spikelets 3–13 mm long; oblong, or ovate; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus present (pubescent).

Glumes more or less equal; about equalling the spikelets; long relative to the adjacent lemmas; pointed (acute or acuminate); mucronate, awnless; carinate; membranous, similar. Lower glume much exceeding the lowest lemma; 1 nerved, or 2–7 nerved. Upper glume 1 nerved, or 2–7 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless.

Female-fertile florets 5–12. Lemmas elliptic; chartaceous, decidedly firmer than the glumes; not becoming indurated; entire to incised; when incised, not deeply cleft (dentate); awnless, or mucronate; non-carinate (?); 3 nerved. Palea present; relatively long to conspicuous but relatively short (not widened or bowed below, i.e unlike Tridens); 2-keeled. Palea back glabrous, or hairy. Palea keels glabrous to scabrous.

Fruit, embryo and seedling. Disseminule a free caryopsis. Fruit oblong; longitudinally grooved (deeply grooved to folded on the side of the hilum); compressed dorsiventrally; sculptured (reticulate). Pericarp fused.

Abaxial leaf blade epidermis. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; chloridoid-type. Costal silica bodies present and well developed; ‘panicoid-type’.

Transverse section of leaf blade, physiology. Combined sclerenchyma girders present; forming ‘figures’ (I's, the sclerenchyma almost filling the adaxial ribs). The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): not described separately. Soreng et al. (2015): Chloridoideae; Cynodonteae; Gouiniinae. 2 species (T. eragrostoides, T. mutica).

Distribution, phytogeography, ecology. North, Central and South America, Caribbean.

On clay, sandy and rocky soils in arid places.

References, etc. Morphological/taxonomic: Grassbase (2016). Leaf anatomical: from Metcalfe’s (1960) summary of Burbidge’s (1945) account of Tridens mutica.

Special comments. Anatomical data wanting. Illustrations. • T. eragrostoides, as Tridens: Hitchcock and Chase (1950). • T. mutica, as Tridens: 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.’.