| # The grass genera of the world |

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

### Triscenia Griseb.

Habit, vegetative morphology. Perennial; caespitose. Culms 20–50 cm high; herbaceous; unbranched above. Culm internodes hollow. Leaves mostly basal. Leaf blades narrow; setaceous (or filiform); acicular (reduced to the midrib); not pseudopetiolate; without cross venation.

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

Inflorescence. Inflorescence of spicate main branches; contracted (the few-spikeleted, ascending branches distant). Primary inflorescence branches 3–5. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’ (the spikelets appressed); solitary; persistent. Spikelets secund (?); shortly pedicellate (the pedicels slender).

Female-fertile spikelets. Spikelets 3 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large; very unequal (G1 about half as long as the G2); (the upper) about equalling the spikelets; (the upper) long relative to the adjacent lemmas; hairless; pointed (G1 acute, G2 acuminate); awnless; non-carinate. Lower glume about 0.5 times the length of the upper glume; 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless (similar to G2); 3 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas narrow, rather acuminate, chartaceous with firm, flat margins; less firm than the glumes to similar in texture to the glumes (thin, but papery); not becoming indurated; entire; pointed; awnless; hairless; glabrous; non-carinate; having the margins lying flat on the palea (‘palea nearly enclosed in flat edges of lemma’); without a germination flap; 3 nerved. Palea present; relatively long; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Embryo small (see Pilger).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much smaller); of similar wall thickness costally and intercostally (rather thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type (rather broad); 54–66 microns long; (7.5–)8.4–11.4(–11.7) microns wide at the septum. Microhair total length/width at septum 4.7–7.8. Microhair apical cells (28.5–)31.5–39(–42) microns long. Microhair apical cell/total length ratio 0.5–0.64. Stomata common; 36–40.5 microns long. Subsidiaries triangular (low, but consistently with points). Guard-cells overlapping to flush with the interstomatals (overlapping). Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies oryzoid-type (apparently, though mostly incompletely developed in material seen). Costal zones with short-cells. Costal short-cells predominantly paired. Costal silica bodies mostly poorly developed; ‘panicoid-type’; cross shaped, dumb-bell shaped, and nodular (mostly poorly developed, in the material seen); not sharp-pointed.

Transverse section of leaf blade, physiology. Leaf blades consisting of midrib.

C3; XyMS+. Mesophyll without adaxial palisade. Midrib having a conventional arc of bundles (the leaf having a deep, u-shaped arc comprising three primaries and four small bundles); with colourless mesophyll adaxially (the centre of the leaf blade occupied by colourless ‘pith’, in which the bundles are embedded, these being in contact with the peripheral chlorenchyma only via their abaxial sclerenchyma girders). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (no adaxial sclerenchyma). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Arthropogoninae. 1 species (T. ovina).

Distribution, phytogeography, ecology. Cuba.

Streamsides.

References, etc. Leaf anatomical: studied by us.

Special comments. Fruit data wanting.

Illustrations. • Triscenia ovina: Hitchcock, Misc. Publ. USDA 243 (1936).

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: 15th June 2025. delta-intkey.com’.

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