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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 (M. mucronata).

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). • M. mucronata: Rose Innes, Ghana Grasses (1977). • General aspect (M. mucronata): Gibbs Russell et al., 1990

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.’.