| # The grass genera of the world |

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

### Tetrachaete Chiov.

Habit, vegetative morphology. Wiry annual; loosely caespitose. Culms 4–25 cm high; herbaceous. Culm nodes glabrous. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; setaceous to not setaceous; flat, or rolled (convolute); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane, or a fringe of hairs.

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

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (from an inflated sheath, a short spike of twin-spikelet glomerules, each glomerule comprising a pair of spikelets subtended by an involucre of four glumes). Inflorescence with axes ending in spikelets (or at least, in terminal glomerules). Inflorescence spatheate (via an inflated upper sheath with reduced lamina); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (to the glomerules); disarticulating; falling entire (i.e., the glomerules disarticulate from the persistent main axis). Spikelets paired; not secund (the glomerules spiralled on the slender rachis); sessile.

Female-fertile spikelets. Spikelets 3–4 mm long; compressed dorsiventrally; falling with the glumes (in the glomerules). Rachilla minutely prolonged beyond the uppermost female-fertile floret; the rachilla extension naked. Hairy callus present (at the base of the glomerule).

Glumes two; relatively large (awn-like, to 1.5 cm long, bending out-wards); more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (far exceeding it); slightly joined; lateral to the rachis (relative to the spikelet, both being behind the lemma); hairy (densely pilose around the spikelets, scabrid above); awned (awn-like); similar (identical). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas saccate (gibbous); less firm than the glumes (firmly membranous); not becoming indurated; entire; pointed; awned (attenuate into a 4 mm awn). Awns 1; median; apical; non-geniculate; much longer than the body of the lemma. Lemmas hairy (pilose, especially on the veins); strongly carinate; without a germination flap; 3 nerved. Palea present; relatively long; 2-nerved (acuminate, minutely pubescent); 2-keeled. Lodicules absent (seemingly). Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2 mm long); sub-triquetrous; sculptured. Hilum short. Pericarp fused. Embryo large.

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; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 21–27 microns long. Microhair basal cells 15 microns long. Microhairs 6–8.4 microns wide at the septum. Microhair total length/width at septum 2.7–3.6. Microhair apical cells 6.6–9 microns long. Microhair apical cell/total length ratio 0.31–0.4. Stomata common; 18–21 microns long. Subsidiaries triangular (mostly with truncated apices). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (small); silicified. Intercostal silica bodies present and perfectly developed; panicoid type. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped and dumb-bell 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 abaxially only. PCR sheath extensions absent. Leaf blade with distinct, prominent adaxial ribs to ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Unioliinae. 1 species (T. elionuroides).

Distribution, phytogeography, ecology. Eritrea, Arabia.

Xerophytic; species of open habitats. Dry stony slopes.

References, etc. Leaf anatomical: studied by us.

Illustrations. • Tetrachaete elionuroides: Nat. Pflanzenfam. Suppl. 2 (1908). • Tetrachaete elionuroides, 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: 15th June 2025. delta-intkey.com’.

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