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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)


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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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