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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: studied by us - S. nervosa (Rottb.) Stapf.

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

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.’.