| # The grass genera of the world |

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

### Tetrachne Nees

Habit, vegetative morphology. Perennial; forming large tufts, the shoots crowded on a short, oblique rhizome. Culms 30–100 cm high; herbaceous; to 0.3 cm in diameter; branched above to unbranched above. Culm nodes glabrous. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate. Leaf blades linear; narrow; 1–4 mm wide; setaceous; usually rolled; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs (dense); about 1 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. Viviparous, or not viviparous.

Inflorescence. Inflorescence of spicate main branches (the few to many branches appressed, short, dense). Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. The racemes spikelet bearing to the base. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate (on one side of rachis, crowded); very shortly pedicellate; densely imbricate.

Female-fertile spikelets. Spikelets 4–6 mm long; adaxial; compressed laterally; falling with the glumes; not disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent. Callus absent.

Glumes two; more or less equal; shorter than the adjacent lemmas; lateral to the rachis; hairless (scabrid on the keels); pointed; awnless; carinate; the keels somewhat winged; similar (thin, acute, the lower smaller). Lower glume shorter than the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awnless. Spikelets with proximal incomplete florets. The proximal incomplete florets 2; epaleate; sterile. The proximal lemmas awnless; 1–3 nerved; exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas (membranous); not becoming indurated (similar to the glumes, but rather larger).

Female-fertile florets 3–5. Lemmas similar in texture to the glumes; not becoming indurated; entire; pointed; awnless; hairless; glabrous (scabrous on the keels); carinate. The keel slightly winged (cf. the glumes). Lemmas having the margins lying flat on the palea; without a germination flap; 5 nerved. Palea present; relatively long (equalling the lemma); entire; awnless, without apical setae; textured like the lemma; not indurated (thin); 2-nerved; 2-keeled. Palea keels winged; scabrous. Lodicules present; 2; free; fleshy; glabrous; heavily vascularized. Stamens 3. Anthers 2 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2.5 mm long); fusiform; slightly compressed laterally. Hilum short. Pericarp fused, or loosely adherent (removable with difficulty after soaking). Embryo large (about 2/3 the length of the fruit); not waisted.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type and chloridoid-type (material seen has a mixture of panicoid type and more or less chloridoid type - but the apical cells are thin walled and often collapsed or missing). Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs (24–)27–30 microns long. Microhair basal cells 15 microns long. Microhairs 6–6.9 microns wide at the septum. Microhair total length/width at septum 3.9–5. Microhair apical cells (9–)12–13.5 microns long. Microhair apical cell/total length ratio 0.38–0.45. Stomata common; 21–24 microns long. Subsidiaries dome-shaped and triangular (mostly domes). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies present and perfectly developed; saddle shaped. Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; saddle shaped (small), or crescentic (a few, and intermediates with saddles); not sharp-pointed.

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

C4; XyMS+. PCR sheath outlines fairly even. 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; traversed by columns of colourless mesophyll cells (the columns often wide, cf. Aristida). Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section; with the ribs more or less constant in size (low, round-topped). Midrib conspicuous to not readily distinguishable; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linking with colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries- the others with strands only); forming ‘figures’. Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups. 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; Eragrostideae; Unioliinae. 1 species (T. dregei).

Distribution, phytogeography, ecology. South Africa and Pakistan.

Mesophytic (often in alluvial soil); species of open habitats; glycophytic. In high altitude grassland.

References, etc. Leaf anatomical: studied by us.

Special comments. Some cultivated specimens hint at hybridization with Fingerhuthia.

Illustrations. • General aspect (Tetrachne dregei): Gibbs Russell et al., 1990. • Tetrachne dregei: Nicora & Rúgolo de Agrasar (1987). • Tetrachne dregei, abaxial epidermis of leaf blade: this project. • Tetrachne dregei, TS 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: 15th June 2025. delta-intkey.com’.

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