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The grass genera of the world

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

Tetrapogon Desf.

Including Codonachne Steud., Cryptochloris Benth., Lepidopironia A. Rich.

Habit, vegetative morphology. Annual, or perennial; stoloniferous, or caespitose. Culms 13–85 cm high; herbaceous. Culm nodes glabrous (pale or dark). The shoots not aromatic. Leaves not basally aggregated; non-auriculate. Sheath margins free. The sheaths keeled. Leaf blades linear (tapered); narrow; usually folded; without abaxial multicellular glands; without cross venation. Ligule a fringed membrane; very narrow.

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

Inflorescence. Inflorescence a single spike, or of spicate main branches (comprising 1–3 upright racemes or spikes, of which 2 may be partly or completely fused along their backs); digitate, or subdigitate, or non-digitate. Primary inflorescence branches 1–3. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary, or paired; secund (the rachis one-sided); biseriate; subsessile.

Female-fertile spikelets. Spikelets 2.5–12 mm long; cuneate; compressed laterally; disarticulating above the glumes (the glumes persistent); not disarticulating between the florets, or disarticulating between the florets (but under the fertile florets only). Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus present.

Glumes two; relatively large; more or less equal; long relative to the adjacent lemmas; hairless; glabrous; pointed (acute or acuminate); awned (awn-tipped), or awnless; carinate; similar (lanceolate, long-pointed, subhyaline). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1–4; awned.

Female-fertile florets 2–7. Lemmas decidedly firmer than the glumes (herbaceous, leathery, the margins hyaline); not becoming indurated; entire (truncate), or incised; when entire blunt; not deeply cleft; awned. Awns 1; median; dorsal; from near the top; non-geniculate; much longer than the body of the lemma. Lemmas hairy (on the back, the margins glabrous); carinate; 3–5 nerved. Palea present; relatively long; apically notched; awnless, without apical setae; not indurated (membranous, sometimes hairy); 2-nerved; 2-keeled. Palea keels hairy (ciliate). Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 0.5–0.7 mm long; not penicillate. Ovary apically glabrous. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.5–3 mm long); ellipsoid; compressed laterally (in one species), or compressed dorsiventrally. Hilum short. Pericarp free. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae small, consisting of one oblique swelling per cell. Mid-intercostal long-cells rectangular; having markedly sinuous walls (coarsely so). Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 18–21 microns long. Microhair basal cells 15 microns long. Microhairs (6–)7.2–8.4 microns wide at the septum. Microhair total length/width at septum 2.1–3. Microhair apical cells (7.5–)9–10.5 microns long. Microhair apical cell/total length ratio 0.42–0.58. Stomata common; 13.5–15 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; exclusively saddle shaped; 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 both abaxially and adaxially. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section to adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans (mostly, with deeply penetrating median cells), or associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); forming ‘figures’ (in the primaries). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Cytology. Chromosome base number, x = 10. 2n = 20. 2 ploid. Chromosomes ‘small’.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 5–6 species.

Distribution, phytogeography, ecology. Mediterranean to India, tropical and South Africa.

Helophytic to mesophytic; shade species, or species of open habitats; glycophytic. Savanna.

Economic aspects. Important native pasture species: T. tenellus (and other species potentially useful), in dry places.

References, etc. Morphological/taxonomic: Launert 1970. Leaf anatomical: studied by us - Tetrapogon tenellus Chiov.

Illustrations. • T. cenchriformis, as Lepidopironia: Richard, Voyage en Abyssinie (1851). • T. cenchriformis, as Cryptochloris spathacea: Hook. Ic. Pl. 14 (1880–82). • General aspect (T. tenellus): Gibbs Russell et al., 1990. • T. tenellus, abaxial epidermis of leaf blade: this project. • T. tenellus, TS 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.’.