The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms 40–110 cm high; herbaceous; unbranched above. Culm nodes hairy, or glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Sheaths hairy or glabrous, striate. Leaf blades linear to linear-lanceolate; narrow; (1–)1.5–9(–10) mm wide; setaceous (at least, tapering to filiform in A. tristachya), or not setaceous; pseudopetiolate (narrow at the base, tapering to it in A. tristachya); without cross venation. Ligule an unfringed membrane (shortly laciniate), or a fringed membrane; 0.3–1.2 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence ambiguously of spicate main branches, or a false spike, with spikelets on contracted axes, or paniculate (spiciform, of appressed or slightly divergent short racemes); contracted; spicate, or more or less irregular; non-digitate. Rachides triquetrous, neither flattened nor hollowed, not winged. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes racemes. The racemes spikelet bearing to the base. Spikelet-bearing axes persistent. Spikelets not secund (congested on the axes); biseriate; shortly pedicellate, or subsessile (the pedicels pilose).
Female-fertile spikelets. Spikelets 2.6–3.6 mm long; narrowly elliptic, or elliptic; abaxial, or adaxial (?); compressed dorsiventrally; biconvex; falling with the glumes. The upper floret not stipitate. Rachilla terminated by a female-fertile floret.
Glumes present; one per spikelet, or two (usually); very unequal (the lower being very small, said to be sometimes absent); about equalling the spikelets (i.e. the upper glumes); (the upper) long relative to the adjacent lemmas (sometimes enclosing the tip of the upper lemma); hairy (with tuberculate whitish hairs); awnless; non-carinate; very dissimilar (the lower reduced). Lower glume when present, much shorter than the lowest lemma; 0 nerved, or 1–3 nerved. Upper glume 5–7(–9) nerved. 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 (hyaline); narrowly ovoid to ellipsoid. The proximal incomplete florets male. The proximal lemmas glumiform; awnless; 5–7(–9) nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas (as long as the spikelet); less firm than the female-fertile lemmas (and stiffly pilose).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (thinly crustaceous); smooth; becoming indurated; white in fruit (or whitish); entire; awnless; hairy (sometimes pubescent at the apex), or hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap. Palea present; relatively long; gaping; entire; awnless, without apical setae; thinner than the lemma to textured like the lemma (cartilaginous); indurated; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit not grooved. Hilum short (punctifom or oblong).
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower). Mid-intercostal long-cells rectangular and fusiform (and often rather irregular, sometimes with oblique end-walls); having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type; 32–60 microns long. Stomata common; 19–32 microns long. Subsidiaries dome-shaped and triangular (variously truncated). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows, or conspicuously in long rows and neither distinctly grouped into long rows nor predominantly paired (in A. tristachya). Costal silica bodies panicoid-type; dumb-bell shaped, or nodular (mostly, in A tristachya).
Transverse section of leaf blade, physiology. Leaf blades seemingly consisting of midrib (in the material of A. trachystachya seen, the lateral laminae being reduced to tiny flanges), or laminar.
C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with arm cells, or without arm cells. Leaf blade with distinct, prominent adaxial ribs, or adaxially flat. Midrib conspicuous; having a conventional arc of bundles (or the bundles forming almost a circle in the reduced blade of A. tristachya); with colourless mesophyll adaxially (and in A. tristachya filling the centre of the vascular ring). Bulliforms present in discrete, regular adaxial groups (in the species other than A tristachya); in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present, or absent (A. tristachya exhibiting abaxial girders only, with the main bundles); when present, forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10. 2n = 20, 40, and 41. 2 and 4 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Paspalinae. 4 species.
Distribution, phytogeography, ecology. Brazil to Argentina.
Species of open habitats; glycophytic. Savanna.
References, etc. Morphological/taxonomic: Parodi 1938; Morrone et al. 1993. Leaf anatomical: studied by us - A. trachystachya (Nees) Pilger; Morrone et al. 1993.
Special comments. Cf. Urochloa and Brachiaria. Fruit data wanting. Illustrations. • A. fiebrigii: Nicora & Rúgolo de Agrasar (1987). • A. trachystachya: 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. delta-intkey.com/grass’.