The grass genera of the world
Type species: Type: A. distachya J.Presl = A. semialata (R.Br.) Hitchc.
Including Bluffia Nees, Coridochloa Nees, Holosetum Steud., Mezochloa Butzin, Pterochlaena Chiov.
Habit, vegetative morphology. Annual (rarely), or perennial; caespitose, or decumbent. Culms 20–150 cm high; herbaceous; unbranched above; tuberous, or not tuberous. Culm nodes hairy, or glabrous. Culm leaf sheaths rounded. Culm internodes hollow. The shoots aromatic (sometimes, coumarin-scented), or not aromatic. Leaves mostly basal; non-auriculate. Leaf blades linear to lanceolate; broad, or narrow; cordate, or not cordate, not sagittate; without cross venation; persistent; rolled in bud. Ligule a fringed membrane to a fringe of hairs. Contra-ligule present (in A. semialata), or absent (?).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches; digitate, or subdigitate (the branches in whorls on a short central axis). Primary inflorescence branches inserted all around the main axis. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets in triplets, or paired; secund. Pedicel apices cupuliform. Spikelets consistently in long-and-short combinations.
Female-fertile spikelets. Spikelets 2.5–7 mm long; lanceolate, or ovate; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret, or prolonged beyond the uppermost female-fertile floret (sometimes, minutely so); the rachilla extension when present, naked. Hairy callus absent.
Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairy (G2 ciliate marginally); pointed; awned, or awnless; very dissimilar (G1 smaller, thinner, often mucronulate, the G2 densely ciliate). Lower glume 3–5 nerved. Upper glume 5 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 reduced (deeply bifid, 1-nerved). The proximal incomplete florets male. The proximal lemmas awned (in Mezochloa = A. paniculata), or awnless; (3–)5 nerved (3 nerved in Mezochloa); similar in texture to the female-fertile lemmas (but with a hyaline zone at the base); not becoming indurated.
Female-fertile florets 1. Lemmas long-attenuate into an awn or mucro; similar in texture to the glumes; smooth to striate; not becoming indurated; yellow in fruit; entire; pointed; mucronate to awned. Awns when present, 1; apical; non-geniculate; hairless (scabrid); much shorter than the body of the lemma to about as long as the body of the lemma. Lemmas hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5 nerved (usually), or 1–3 nerved (Mezochloa). Palea present (auriculate at base); relatively long; entire; awnless, without apical setae; 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm hard; containing only simple starch grains. Embryo without an epiblast.
Seedling with a short mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved; 21–23 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present; panicoid-type; (48–)50–66(–69) microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 8–11. Microhair apical cells (21–)24–34(–36) microns long. Microhair apical cell/total length ratio 0.35–0.61. Stomata common; 34.5–36 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (in A. semialata), or absent or very rare; not paired (solitary); not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; butterfly shaped, or dumb-bell shaped, or nodular.
Transverse section of leaf blade, physiology. C4 (in all the material examined except A. semialata ssp. eckloniana, including Coridochloa), or C3 (A. semialata ssp. eckloniana). The anatomical organization when C4 unconventional. Organization of PCR tissue when C4 Alloteropsis type (with an inner PCR sheath, and an outer sparsely chlorenchymatous sheath of unknown function). Biochemical type PCK (in Australian C4 A. semialata ssp. semialata), or NADPME (in southern African C4 A. semialata: evidently more biochemical typing is needed, given the intergrading C4 anatomical forms, the NAD-ME anatomy of some species yet to be biochemically typed, and the problematical taxonomy); XyMS+ (A. cimicina, A. quintasii, A. latifolia, A. paniculata, A. papillosa), or XyMS (in C4 forms of A. semialata, plus A. angusta, A. homblei, A. gwebiensis). PCR sheath outlines when applicable uneven, or even. PCR sheath extensions when applicable present. Maximum number of extension cells 3. PCR cells of A. semialata with a suberised lamella. PCR cell chloroplasts of A. semialata ovoid; with well developed grana; centrifugal/peripheral (or evenly distributed, in A. semialata ssp. semialata, A. angusta, A. homblei and A. gwebiensis), or centripetal (in A. cimicina, A. quintasii, A. latifolia, A. paniculata and A. papillosa, which are anatomically indicated as NAD-ME). Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma. Leaf blade nodular in section to adaxially flat; with the ribs more or less constant in size. Midrib conspicuous, or not readily distinguishable; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially, or without colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present, or absent; forming figures, or nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Phytochemistry. Leaf blade chlorophyll a:b ratio of Australian C4 A. semialata 3.36–3.63.
Cytology. Chromosome base number, x = 9. 2n = 18 (C3 A. semialata), or 54 (C4 A. semialata).
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Boivinellinae. 5–8 species (with complexes around A. semialata and A. paniculata reflected in specific and generic synomyms).
Distribution, phytogeography, ecology. Tropical Africa, Asia & Australia.
Helophytic, or mesophytic, or xerophytic; species of open habitats; glycophytic. Marshy and weedy places.
Economic aspects. Important native pasture species: A. semialata.
References, etc. Morphological/taxonomic: Gibbs Russell 1983. Leaf anatomical: Metcalfe 1960; Ellis 1974; Hattersley et al. 1977; Hattersley and Long 1990; this project.
Illustrations. • A. cimicina, as Urochloa: Kunth (1835). • A. semialata: Gardner, 1952. • A. semialata, general aspect: Gibbs Russell et al., 1990. • Spikelets in situ (A. semialata). • Spikelet in situ (A. semialata). • Leaf blade T.S. of A. semialata, fluorescence image (1). • Leaf blade T.S. of A. semialata, fluorescence image (2). • Leaf blade T.S.: immunofluorescent-labelled Rubisco in A. semialata (Hattersley, Watson and Osmond 1977)
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: 13th November 2017. delta-intkey.com/grass’.