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The grass genera of the world

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

Trigonochloa P.M. Peterson & N. Snow

~ Leptochloa

Type species: T. uniflora (Chipp.) P.M. Peterson & N. Snow.

Habit, vegetative morphology. Annual to perennial (short-lived); rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 15–130 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Leaf blades broad to narrow; (1-)13(-17 cm long, 0.3–14(–19) mm wide; flat. Ligule an unfringed membrane (becoming irregularly lacerate).

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

Inflorescence. Inflorescence of spicate main branches; non-digitate. Primary inflorescence branches inserted all around the main axis (with the spicate 1.5–7cm long branches scattered along the central axis). Spikelets subsessile; imbricate (overlapping).

Female-fertile spikelets. Spikelets 1.9–2.8 mm long; compressed laterally; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret, or terminated by a female-fertile floret (?).

Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; pointed (acute to acuminate); mucronate or not, awnless; linear to narrowly ovate, similar. Lower glume about equalling the lowest lemma to much exceeding the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets without proximal incomplete florets.

Female-fertile florets 1–2. Lemmas ovate; thinly membranous to hyaline, not becoming indurated; entire; pointed (acute); crested at the tip; minutely hairy (along the nerves); 3 nerved. Palea present; relatively long; 2-keeled. Palea keels ciliolate. Stamens 3.

Fruit, embryo and seedling. Fruit light brown; narrowly ellipsoid; longitudinally grooved; smooth to slightly rugose-striate. Pericarp fused.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Long-cells differing markedly in wall thickness costally and intercostally (thicker intercostally). Intercostal zones with typical long-cells, or exhibiting many atypical long-cells (many long-cells very short). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; nearly always clearly two-celled, or ostensibly one-celled (rarely); chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Stomata common; 15–25.5 microns long. Subsidiaries low dome-shaped to triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (solitary); silicified, or not silicified. Intercostal silica bodies absent, or imperfectly developed. Costal silica bodies present in alternate cell files of the costal zones; not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines uneven, or even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib fairly conspicuous; with one bundle only; with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Cytology. 2n = 36.

Classification. Watson & Dallwitz (1994): not described separately. Soreng et al. (2015): Chloridoideae; Cynodonteae; Perotidinae. 2 species (T. rupestris, T. uniflora).

Distribution, phytogeography, ecology. Southern Africa east to India and Sri Lanka.

References, etc. Morphological/taxonomic: Peterson, P.M. & Snow, N. (2012). PhytoKeys 13: 25–38. Leaf anatomical: studied by us (but slides of T. uniflora to be re-examined); Metcalfe (1960).

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.’.