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The grass genera of the world

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

Tricholaena Schrad.

From the Greek thrix, trichos (a hair) and chlaena (mantle), referring to silky spikelets.

Excluding Rhynchelytrum

Habit, vegetative morphology. Annual (rarely), or perennial; caespitose, or decumbent. Culms 10–120 cm high; herbaceous; unbranched above. Culm internodes hollow. Leaf blades often glaucous-inrolled, rigid; without cross venation. Ligule a fringed membrane (very narrow), or a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence paniculate; open, or contracted; with capillary branchlets (these flexuous); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 2–3.5 mm long; compressed laterally; with a distinctly elongated rachilla internode between the glumes (having G1 slightly separated from G2). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes present; one per spikelet, or two; very unequal; (the longer) long relative to the adjacent lemmas; free; hairy (the upper and/or both sometimes variously hairy), or hairless; awnless (the upper sometimes mucronate); very dissimilar (the lower often reduced to a tiny scale, hairy or glabrous), or similar (rarely). Lower glume about 0.1–0.2 times the length of the upper glume; 0–1 nerved. Upper glume indistinctly 3 nerved, or 5 nerved (thinly membranous, emarginate to acute). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas awnless; 3–7 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (often hairy, resembling the upper glume); not becoming indurated.

Female-fertile florets 1 (dorsally compressed). Lemmas decidedly firmer than the glumes (cartilaginous to sub-crustaceous); smooth; becoming indurated to not becoming indurated; entire to incised; not deeply cleft (obtuse to emarginate); awnless; hairless (shiny); non-carinate; having the margins lying flat on the palea; 3–5 nerved. Palea present; relatively long; tightly clasped by the lemma; entire; textured like the lemma; 2-nerved. Lodicules present; 2; free; glabrous; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles fused, or free to their bases.

Fruit, embryo and seedling. Fruit free from both lemma and palea (but enclosed); compressed dorsiventrally. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type; 51–66 microns long; 5.4–6 microns wide at the septum. Microhair total length/width at septum 8.5–12.2. Microhair apical cells 24–39 microns long. Microhair apical cell/total length ratio 0.47–0.59. Stomata common; 30–36 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs. Costal zones with short-cells. Costal short-cells mixture on the one epidermis. Costal silica bodies ‘panicoid-type’; cross shaped (some), or nodular (mostly); not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS+. PCR sheath outlines uneven. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section to adaxially flat; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only to having a conventional arc of bundles (depending on delimitation of mid-rib). Bulliforms present in discrete, regular adaxial groups; in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 9. 2n = 36. 4 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae (Melinideae). Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Melidininae. 12 species.

Distribution, phytogeography, ecology. Africa, Madagascar, Canaries, Mediterranean.

Xerophytic; species of open habitats; glycophytic. Sandy and stony soil, sometimes ruderal.

Economic aspects. Important native pasture species: T. teneriffae.

Rusts and smuts. Rusts — Physopella. Smuts from Ustilaginaceae. Ustilaginaceae — Sphacelotheca and Ustilago.

References, etc. Leaf anatomical: studied by us - T. monachne (Trin.) Stapf & Hubbard, T. teneriffae Parl.

Illustrations. • T. monachne, as Xylochlaena: Hook. Ic. Pl. 31 (1922). • T. teneriffae: Jacques-Félix, 1962. • General aspect (T. monachne): Gibbs Russell et al., 1990. • T. monachne, abaxial epidermis of leaf blade: this project

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.’.