The grass genera of the world
Including Anthaenantia P. Beauv. (alternative spelling), Aulaxanthus Elliott, Aulaxia Nutt
Habit, vegetative morphology. Perennial; caespitose. Culms 60–120 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal; non-auriculate. Leaf blades narrow (3–5 mm); without cross venation; disarticulating from the sheaths (from the upper culms). Ligule present; a fringed membrane (short); 0.5 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open; with capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 3 mm long; elliptic; compressed dorsiventrally (but with the side of the lower lemma somewhat flattened); disarticulating above the glumes, or falling with the glumes, or not disarticulating. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes one per spikelet (the upper); relatively large; long relative to the adjacent lemmas; hairy (with longitudinal rows of dense hairs); pointed; awnless; non-carinate. 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; male. The proximal lemmas awnless; 5 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas (also with longitudinal rows of hairs); not becoming indurated.
Female-fertile florets 1. Lemmas more or less boat-shaped and firm to the tip, by contrast with Leptocoryphium; decidedly firmer than the glumes; not becoming indurated (cartilaginous, dark brown); entire; pointed; awnless; hairless; carinate to non-carinate; having the margins lying flat on the palea; with a clear germination flap; 3–5 nerved. Palea present; relatively long; awnless, without apical setae; keel-less. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Embryo large. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired; silicified. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type.
Transverse section of leaf blade, physiology. C4; XyMS. Mesophyll with non-radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs, or nodular in section; with the ribs more or less constant in size. Midrib not readily distinguishable; having a conventional arc of bundles (in the blade, the smallest bundles are in an abaxial row, with the medium-sized ones above them in the ribs (phloem always abaxial): c.f. Leptocoryphium); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10 (?). 2n = 20.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Otachyriinae. 2 species.
Distribution, phytogeography, ecology. Warm America.
Economic aspects. Important native pasture species: A. rufa.
References, etc. Leaf anatomical: studied by us - A. rufa (Ell.) Schult.
Illustrations. • A. villosa, as Panicum ignoratum: Kunth (1835). • A. villosa: Hitchcock and Chase (1950)
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’.