The grass genera of the world
Habit, vegetative morphology. Annual (rarely), or perennial; caespitose. Culms 60–250 cm high; herbaceous (erect); unbranched above. Culm nodes glabrous. Culm internodes solid. Young shoots intravaginal. The shoots aromatic (and with a strong bitter taste), or not aromatic. Leaves mostly basal, or not basally aggregated; auriculate (the auricles from the sheaths, glabrous or hairy). Leaf blades linear; broad, or narrow; flat, or rolled (convolute); without cross venation; persistent. Ligule an unfringed membrane; not truncate (apically rounded); 2–5 mm long.
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; overtly heteromorphic (the pedicellate spikelet usually with a long-awned G1); all in heterogamous combinations.
Inflorescence. Inflorescence of spicate main branches, or a single raceme (of one to many long, rigid, spiciform, cylindrical or slightly flattened racemes); digitate, or non-digitate (when the raceme solitary). Rachides hollowed and flattened. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes racemes (these long, many-noded); the spikelet-bearing axes with more than 10 spikelet-bearing articles (up to 35). The racemes spikelet bearing to the base. Spikelet-bearing axes solitary to clustered; with substantial rachides; disarticulating; disarticulating at the joints. Articles non-linear (clavate); with a basal callus-knob; appendaged; disarticulating obliquely; somewhat hairy, or glabrous. Spikelets paired; sessile and pedicellate (the pedicels resembling the internodes); 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 (very rarely with one floret hermaphrodite), or sterile.
Female-sterile spikelets. The pedicelled spikelets with a conspicuously long-awned G1. Having two florets, usually both male, very occasionally one hermaphrodite. Sometimes sterile and reduced to the glumes. The male spikelets with glumes (the G1 conspicuously awned); 2 floreted (usually both male).
Female-fertile spikelets. Spikelets 5–10 mm long; abaxial; compressed dorsiventrally; planoconvex; falling with the glumes (and with the adjacent joint and pedicel); not disarticulating between the florets; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long (but concealed by the joint until the raceme disarticulates); blunt.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (larger than them); dorsiventral to the rachis; hairy (G1), or hairless (G2); without conspicuous tufts or rows of hairs; pointed; awned (G1 occasionally bi-aristulate), or awnless; carinate (G2), or non-carinate (G1); very dissimilar (the G1 leathery, dorsally flattened, 2-keeled, the G2 thinner, naviculate-keeled). Lower glume much exceeding the lowest lemma; two-keeled; flattened on the back; not pitted; relatively smooth, or relatively smooth and muricate; obscurely 5–7 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed. The proximal incomplete florets male. The proximal lemmas awnless; 2 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; pointed, or blunt; awnless; hairless; non-carinate; without a germination flap; 2–5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; not indurated (hyaline); 2-nerved; flat backed. Lodicules present; 2; free; fleshy; glabrous; not toothed. Stamens 3. Anthers 1.5–4 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (about 3–4 mm long); ellipsoid. Hilum short. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae not over-arching the stomata; consisting of one oblique swelling per cell (conspicuiously so on the interstomatals). Mid-intercostal long-cells rectangular; having markedly sinuous walls and having straight or only gently undulating walls. Microhairs present; panicoid-type; 57–66 microns long; (6.6–)7.5–8.4(–9) microns wide at the septum. Microhair total length/width at septum 6.7–9.1. Microhair apical cells 28.5–36 microns long. Microhair apical cell/total length ratio 0.5–0.55. Stomata common (most grooves with a single row); (42–)43–45(–51) microns long. Subsidiaries dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Costal zones with short-cells. Costal short-cells conspicuously in long rows, or predominantly paired (especially over the midrib). Costal silica bodies panicoid-type; dumb-bell shaped and nodular; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines uneven. PCR cell chloroplasts centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs (and small narrow abaxial ones); with the ribs more or less constant in size (becoming smaller away from the midrib). Midrib conspicuous; having a conventional arc of bundles (a large median, and one or two smaller laterals on either side, according to interpretation of the midrib limits); with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups to not present in discrete, regular adaxial groups (the groups very large); irregularly grouped,sometimes associated with colourless mesophyll cells to form deeply-penetrating fans; associating with colourless mesophyll cells to form arches over small vascular bundles (the arms of the arches sometimes traversing the mesophyll). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries); forming figures (Is and Ts). Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. The lower glume of the pedicellate spikelet with a 510 mm (or longer) awn.
Cytology. Chromosome base number, x = 10. 2n = 20.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 7 species.
Distribution, phytogeography, ecology. South and tropical Africa, Madagascar.
Mesophytic; species of open habitats; glycophytic. Savanna grassland.
Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae Sorosporium.
References, etc. Leaf anatomical: Metcalfe 1960; this project; photos of U. agropyroides provided by R.P. Ellis.
Illustrations. • U. annuum: Jacques-Félix, 1962. • General aspect (U. agropyroides): Gibbs Russell et al., 1990. • U. squarrosum, 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: 13th November 2017. delta-intkey.com/grass’.