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The grass genera of the world

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

Acroceras Stapf

From the Greek akros (at the top) and keras (a horn), alluding to crested lemmas.

Including Neohusnotia A. Camus

Excluding Commelinidium

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or stoloniferous, or decumbent. Culms 10–125 cm high; herbaceous (often much-branched). Leaves non-auriculate. Leaf blades linear-lanceolate to ovate-lanceolate; cordate (somewhat amplexicaul); pseudopetiolate, or not pseudopetiolate; cross veined, or without cross venation. Ligule present (mostly), or absent (rarely); a fringed membrane (very narrow), or a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence of spicate main branches (racemes or panicles), or paniculate; open; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets paired; secund; pedicellate (the pairs of pedicels more or less connate below); consistently in ‘long-and-short’ combinations (at least in lower parts of panicle), or not in distinct ‘long-and-short’ combinations.

Female-fertile spikelets. Spikelets abaxial; compressed laterally to compressed dorsiventrally (terete below); falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; very unequal; (the longer, upper) long relative to the adjacent lemmas (subequalling the L1); dorsiventral to the rachis; awnless; similar (membranous). Lower glume 3 nerved. Upper glume 5–7 nerved, or 8–9 nerved (rarely). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male, or sterile. The proximal lemmas awnless; 5 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas; becoming indurated to not becoming indurated (membranous to crustaceous).

Female-fertile florets 1. Lemmas decidedly firmer than the glumes; smooth to striate; becoming indurated to not becoming indurated; entire; crested at the tip (the green apex blunt, hard, laterally compressed); awnless; hairless (shiny); carinate to non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; gaping (its tip reflexed); awnless, without apical setae; textured like the lemma (firm); indurated to not indurated; 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 ellipsoid; flattened on one side. Hilum short, or long-linear (punctiform, oblong, or linear and half to two thirds the fruit length).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones with typical long-cells, or without typical long-cells (long-cells cubical). Mid-intercostal long-cells having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present; panicoid-type and chloridoid-type; (36–)40–84 microns long; 3.9–6 microns wide at the septum. Microhair total length/width at septum 8–10.8. Microhair apical cells (24–)27–36(–38) microns long. Microhair apical cell/total length ratio 0.42–0.65. Stomata common; 25.5–30 microns long. Subsidiaries triangular. Intercostal short-cells common, or absent or very rare; when seen, in cork/silica-cell pairs; silicified. Intercostal silica bodies cross-shaped and oryzoid-type. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired (rarely). Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; Isachne-type. Leaf blade with distinct, prominent adaxial ribs, or adaxially flat; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only, or having a conventional arc of bundles. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; in simple fans (or the fans ill defined). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 9. 2n = 36.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Boivinellinae. 15 species.

Distribution, phytogeography, ecology. Africa, Madagascar, Indomalayan region.

Commonly adventive. Hydrophytic to mesophytic; shade species and species of open habitats; glycophytic. Shallow water, damp places and forests.

Economic aspects. Significant weed species: A. zizanioides. Cultivated fodder: A. macrum. Important native pasture species: A. macrum.

References, etc. Morphological/taxonomic: Launert 1970; Zuloaga 1987. Leaf anatomical: Metcalfe 1960; studied by us - A. macrum Stapf, A. munroanum (Balansa) Henrard.

Special comments. Fruit data wanting. Illustrations. • A. zizanioides, as Panicum: Kunth (1835). • A. zizanioides, as Panicum: Wood, Natal Plants 2 (1904). • A. macrum, general aspect: Gibbs Russell et al., 1990. • A. macrum, 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: 11th December 2017.’.