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, 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 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 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.
Taxonomy. Panicoideae; Panicodae; Paniceae.
Distribution, ecology, phytogeography. 15 species; Africa, Madagascar, Indomalayan region. Commonly adventive. Hydrophytic to mesophytic; shade species and species of open habitats; glycophytic. Shallow water, damp places and forests.
Paleotropical and Neotropical. African, Madagascan, and Indomalesian. Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, and Malesian. Caribbean, Venezuela and Surinam, Amazon, Central Brazilian, and Pampas. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian.
Economic importance. 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; this project.
Special comments. Fruit data wanting.
Illustrations. • General aspect. • Abaxial epidermis of leaf blade
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
