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From the Greek thrix (hair) and neuron (nerve), re ciliate lemma nerves.
Including Crossotropis Stapf
Habit, vegetative morphology. Annual, or perennial (xeromorphic). Culms 12–100 cm high; herbaceous; branched above (often), or unbranched above. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades linear (pointed); narrow; setaceous, or not setaceous; usually flat; without abaxial multicellular glands; without cross venation. Ligule an unfringed membrane; truncate.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches (the racemes scattered along a central axis); open. Primary inflorescence branches 8–40. Rachides hollowed. Spikelets all partially embedded in the rachis. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate (on two faces of the trigonous rachis); subsessile.
Female-fertile spikelets. Spikelets 5.3–14 mm long; adaxial; 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.
Glumes two; more or less equal; about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; dorsiventral to the rachis; pointed; awned, or awnless (tapered into a mucro or short awn); carinate; similar (narrowly lanceolate, membranous, persistent). Lower glume much exceeding the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.
Female-fertile florets 2–8. Lemmas similar in texture to the glumes (membranous); not becoming indurated; incised; 2 lobed; not deeply cleft (bluntly 2-toothed); mucronate, or awned. Awns when present, 1; from a sinus; non-geniculate; much shorter than the body of the lemma. Lemmas hairy (conspicuously pectinate-ciliate on the lateral nerves); non-carinate (rounded on the back); 3 nerved. Palea present; relatively long; entire to apically notched; awnless, without apical setae; 2-nerved; 2-keeled. Palea keels scabrous, or hairy. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short. Pericarp fused. Embryo large; waisted.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (deeply). Microhairs present; more or less spherical; clearly two-celled; chloridoid-type (basal cell globular, apical cell small). Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs 25–27(–30) microns long. Microhair basal cells 24 microns long. Microhairs (11.4–)12–13.5(–15) microns wide at the septum. Microhair total length/width at septum 1.9–2.4. Microhair apical cells (7.5–)8.4–9(–10.5) microns long. Microhair apical cell/total length ratio 0.28–0.38. Stomata common; 22–26 microns long. Subsidiaries dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Numerous small, papilla-like prickles present. Costal zones with short-cells. Costal short-cells conspicuously in long rows (but short cells often relatively long). Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; dumb-bell shaped (mostly), or cross shaped (few), or nodular (few); not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Leaf blade ‘nodular’ in section to adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (I’s or anchors in all bundles). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 10. 2n = 20. 2 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Trichoneurinae. 7 species.
Distribution, phytogeography, ecology. America, tropical Africa.
Xerophytic; species of open habitats. In sandy or stony soil.
Rusts and smuts. Rusts — Puccinia.
References, etc. Morphological/taxonomic: Phillips 1973. Leaf anatomical: studied by us - T. arenaria (Hochst. & Steud.) Ekman.
Illustrations. • T. grandiglumis, as Crossotropis: Hook. Ic. Pl. 27 (1901). • T. lindleyana, as Leptochloa: Kunth (1835), Dist. méthodique de la famille Graminées. • General aspect of T. grandiglumis: Gibbs Russell et al., 1990. • T. arenaria, 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: 25th January 2024. delta-intkey.com’.
