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The grass genera of the world

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

Megastachya P. Beauv.

Habit, vegetative morphology. Annual (tall, erect), or perennial (weakly); sometimes stoloniferous, or decumbent (forming secondary shoots from the rooting nodes). Culms 30–100 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades linear-lanceolate to lanceolate; broad; to 20 mm wide; cordate (amplexicaul); flat; cross veined (abaxially); persistent. Ligule an unfringed membrane; not truncate; about 0.5 mm long. Contra-ligule absent.

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

Inflorescence. Inflorescence paniculate; open (large, racemose); with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate (the pedicels long and slender).

Female-fertile spikelets. Spikelets 7–15 mm long (becoming smaller acropetally in the spikelet); compressed laterally; disarticulating above the glumes; 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; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous (on the sides), or scabrous (on the mid-nerve); shortly awned (or mucronate, from the excurrent mid-nerve); carinate; similar (membranous-herbaceous, broadly ovate). Lower glume 0.75 times the length of the upper glume; shorter than the lowest lemma; 3–4 nerved. Upper glume 3–4 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped; awnless.

Female-fertile florets 12–17. Lemmas similar in texture to the glumes; not becoming indurated; incised; 2 lobed; not deeply cleft (bidentate); awnless, or mucronate (the mucro from between the lobes, via the excurrent mid-nerve); hairless; glabrous (on the sides), or scabrous (on the mid-nerve); carinate; without a germination flap; obscurely 5–7 nerved. Palea present (narrower than lemma); relatively long; tightly clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea keels hairy. Lodicules absent. Stamens 2–3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2 (long).

Fruit, embryo and seedling. Fruit free from both lemma and palea (but falling with them); small (about 1 mm long); subglobose; triquetrous. Hilum short. Embryo small. Endosperm containing only simple starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells having markedly sinuous walls (coarsely so, the walls thin). Microhairs present; panicoid-type (balanoform); (48–)54–68 microns long. Microhair apical cells 37–58 microns long. Microhair apical cell/total length ratio 0.78. Stomata common. Subsidiaries triangular. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped and dumb-bell shaped, or butterfly shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade; without arm cells (according to Metcalfe 1960), or with arm cells (?); with fusoids (as represented by laterally extended PBS cells). The fusoids an integral part of the PBS. Leaf blade adaxially flat. Midrib conspicuous; having complex vascularization (1 large median with 2 tiny laterals, all enclosed in a common sheath). Bulliforms present in discrete, regular adaxial groups; in simple fans (the fans very wide, occupying most of the epidermis of each intercostal zone). Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 12. 2n = 48. 4 ploid.

Classification. Watson & Dallwitz (1994): Centothecoideae; Centotheceae. Soreng et al. (2015): Panicoideae; Centotheceae. 1 species.

Distribution, phytogeography, ecology. Tropical and southern Africa.

Mesophytic; shade species; glycophytic. In forests.

References, etc. Leaf anatomical: Metcalfe 1960; photos of M. mucronata provided by R.P. Ellis.

Illustrations. • M. mucronata (as owariensis), with Eleusine coracana, Schismus marginatus (= barbatus) and Uniola maritima (= paniculata): P. Beauv. (1812). • General aspect (M. mucronata): Gibbs Russell et al., 1990


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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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