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The grass genera of the world

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

Sehima Forssk.

Including Hologamium Nees

Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 20–100 cm high; herbaceous; branched above, or unbranched above. Culm nodes hairy, or glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; setaceous (rarely), or not setaceous; without cross venation; persistent. Ligule a fringed membrane, or a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic; all in heterogamous combinations.

Inflorescence. Inflorescence a single raceme (a single, curved, culm-like ‘raceme’ with embedded spikelets). Rachides hollowed and flattened. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikelike (laterally compressed, curved); solitary; with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ stoutly linear to subclavate; not appendaged; densely long-hairy (with white hairs ventrally). Spikelets paired; secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.

Female-sterile spikelets. Pedicelled spikelets male or neuter, strongly dorsally compressed, flat, often with the G1 large and strongly nerved, the lemmas awnless. The lemmas awnless.

Female-fertile spikelets. Spikelets slightly compressed dorsiventrally, or compressed laterally and compressed dorsiventrally (commonly more or less square in section); falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present.

Glumes two; more or less equal; long relative to the adjacent lemmas; without conspicuous tufts or rows of hairs; awned (the upper with an apical bristle-like awn, the lower bidentate or 2-mucronate); very dissimilar (the lower 2-keeled and 2-winged, the upper naviculate-subulate and awned). Lower glume two-keeled (scarcely winged); concave on the back, or sulcate on the back; not pitted; relatively smooth; 3–6 nerved. Upper glume 3–6 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas awnless; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; incised; 2 lobed; awned. Awns 1; median; from a sinus; geniculate; hairless to hairy (puberulous to ciliate along its coils); much longer than the body of the lemma. Lemmas hairy (above), or hairless (glabrous); non-carinate; 2–3 nerved. Palea present; relatively long; not indurated (hyaline); 2-nerved. 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; concave on one side; compressed dorsiventrally. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls (conspicuously pitted). Microhairs present; panicoid-type (unusually slender); (63–)72–75(–78) microns long; 3.6–3.9–4.5 microns wide at the septum. Microhair total length/width at septum 14–20.8. Microhair apical cells (24–)30–33(–35) microns long. Microhair apical cell/total length ratio 0.38–0.44. Stomata common; 24–27–30 microns long. Subsidiaries predominantly triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. S. nervosa with abundant prickles. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; short to long dumb-bell shaped (in S. nervosa); not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs very irregular in sizes (major bundles with large adaxial and abaxial ribs, the rest unribbed or with small ribs, in S. nervosa). Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (these large and wide); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the primaries with heavy T’s). Sclerenchyma all associated with vascular bundles.

Phytochemistry. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 10, 17, and 20. 2n = 34 and 40.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Ischaeminae. 5 species.

Distribution, phytogeography, ecology. Warm Africa, India, Australia.

Helophytic to mesophytic; species of open habitats; glycophytic. Savanna, sometimes on heavy clay.

Rusts and smuts. Smuts from Tilletiaceae and from Ustilaginaceae. Tilletiaceae — Entyloma. Ustilaginaceae — Sphacelotheca.

References, etc. Leaf anatomical: this project.

Illustrations. • S. nervosum: Hook. Ic. Pl. 31 (1922). • S. nervosum: Gardner, 1952. • Culm, inflorescence (S. galpinii): Gibbs Russell et al., 1990. • 'Raceme' of S. nervosum


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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: 13th November 2017. delta-intkey.com/grass’.

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