The grass genera of the world
Including Anatherum P. Beauv., Arthrostachys Desv., Arthrolophis (Trin.) Chiov., Dimeiostemon Raf., Eriopodium Hochst., Heterochloa Desv., Homoeatherum Nees, Leptopogon Roberty
Habit, vegetative morphology. Annual, or perennial; rhizomatous, or caespitose, or decumbent. Culms 8–250(–430) cm high; herbaceous; branched above, or unbranched above. The branching suffrutescent (occcasionally), or simple. Culm internodes solid. The shoots not aromatic. Leaves non-auriculate. Leaf blades linear; broad, or narrow; setaceous, or not setaceous; pseudopetiolate, or not pseudopetiolate; without cross venation; rolled in bud, or once-folded in bud. Ligule an unfringed membrane to a fringed membrane. Contra-ligule present (occasionally, of hairs, e.g. A. gayanus), or absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile (the pedicelled spiklet occasionally suppressed); overtly heteromorphic; in both homogamous and heterogamous combinations (the lowermost pair imperfect and homogamous), or all in heterogamous combinations. Plants outbreeding; with hidden cleistogenes, or without hidden cleistogenes. The hidden cleistogenes when present, in the leaf sheaths.
Inflorescence. Inflorescence of spicate main branches, or paniculate (usually with paired or digitate racemes, these often spatheate and aggregated into false panicles). Rachides neither flattened nor hollowed, not winged. Inflorescence usually spatheate; a complex of partial inflorescences and intervening foliar organs (often), or not comprising partial inflorescences and foliar organs. Spikelet-bearing axes racemes; paired (nearly always), or clustered (very rarely only one, the raceme bases terete, often long, hardly ever deflexed); with very slender rachides, or with substantial rachides; disarticulating; disarticulating at the joints. Articles without a basal callus-knob; appendaged, or not appendaged; densely long-hairy (plumose), or somewhat hairy (ciliate), or glabrous (rarely). Spikelets paired; sessile and pedicellate; consistently in long-and-short combinations; in pedicellate/sessile combinations. Pedicels of the pedicellate spikelets free of the rachis. The shorter spikelets hermaphrodite. The longer spikelets male-only, or sterile (sometimes reduced to their pedicels).
Female-sterile spikelets. The pedicelled spikelets male or barren, usually awnless, occasionally suppressed. The lemmas usually awnless.
Female-fertile spikelets. Spikelets compressed laterally, or not noticeably compressed, or compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; blunt.
Glumes two; more or less equal; long relative to the adjacent lemmas; hairy, or hairless; without conspicuous tufts or rows of hairs; awned, or awnless (G2 sometimes aristate); very dissimilar (subleathery to membranous, the lower flat, concave or canaliculate on the back, its margins folded and 2-keeled, the upper naviculate, carinate above). Lower glume two-keeled; flattened on the back to sulcate on the back; not pitted; relatively smooth; 1–11 nerved (sometimes lacking the midnerve). Upper glume 1–3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 2 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 (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (hyaline to firm, sometimes substipitate beneath the awn); not becoming indurated; incised (usually bifid); awned. Awns 1; median; from a sinus; geniculate; hairless (glabrous), or hairy (puberulous); about as long as the body of the lemma to much longer than the body of the lemma. Lemmas hairy, or hairless (often ciliate or ciliolate); non-carinate; 1–3 nerved. Palea present; very reduced (hyaline); not indurated; nerveless. Lodicules present (tiny); 2; free; fleshy; ciliate, or glabrous. Stamens 1–3. Anthers penicillate, or not penicillate. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed laterally, or compressed dorsiventrally, or not noticeably compressed (subterete to planoconvex). Hilum short. Embryo large; waisted. Endosperm hard; without lipid. Embryo with an epiblast (e.g., A. gayanus), or without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina.
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; (24–)27–55 microns long; 6–7.5 microns wide at the septum. Microhair total length/width at septum 3.2–5. Microhair apical cells 15–30 microns long. Microhair apical cell/total length ratio 0.52–0.63. Stomata common; 27–30 microns long. Subsidiaries triangular, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common, or absent or very rare; not paired (mainly solitary); not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; cross shaped, or butterfly shaped, or dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; biochemical type NADPME (3 species); XyMS. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma, or with non-radiate chlorenchyma; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; in irregular groups, or the epidermis exctensively bulliform, or associated with colourless mesophyll cells to form deeply-penetrating fans (then sometimes associated with traversing colourless columns). Many of the smallest vascular bundles unaccompanied by sclerenchyma, or all the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming figures. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles scattered.
Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (5 species).
Cytology. Chromosome base number, x = 5 and 10. 2n = 20, 40, 60, 100, 120, and 180. 2–18 ploid. Chromosomes small. Nucleoli persistent.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. About 100 species.
Distribution, phytogeography, ecology. Tropical.
Commonly adventive. Mesophytic, or xerophytic. Mostly savanna, some in tropical highlands.
Economic aspects. Significant weed species: A. bicornis, A. condensatus, A. gerardii, A. glomeratus, A. lateralis, A. scoparius, A. selloanus, A. ternarius, A. virginicus. Cultivated fodder: A. gayanus. Important native pasture species: A. gerardi, A. scoparius (North America); A. abyssinicus, A. chinensis, A. distachyos, A. lima (Kenya); etc.
Rusts and smuts. Rusts Phakopsora and Puccinia. Taxonomically wide-ranging species: Phakopsora incompleta, Puccinia microspora, Puccinia nakanishikii, Puccinia eritraeensis, Puccinia versicolor, and Uromyces clignyi. Smuts from Ustilaginaceae. Ustilaginaceae Sorosporium, Sphacelotheca, Tolyposporella, and Ustilago.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • A. bicornis, as Anatherum: P. Beauv. (1812). • A. schirensis: Fl. W. Trop. Afr. (1936). • A. chinensis, general aspect: Gibbs Russell et al., 1990. • Abaxial epidermis of leaf blade (A. virginicus)
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: 12th March 2017. delta-intkey.com/grass’.