The grass genera of the world
Habit, vegetative morphology. Perennial; densely caespitose. Culms about 20–100 cm high; herbaceous. Culm nodes glabrous. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Sheaths glabrous. Leaf blades linear; narrow; 2–4 mm wide; flat (at the base), or rolled (convolute above); without cross venation; persistent. Ligule an unfringed membrane; not truncate (rounded to acute).
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets mixed in the inflorescence. The spikelets homomorphic; all in heterogamous combinations (?).
Inflorescence. Inflorescence paniculate; spatheate; a complex of partial inflorescences and intervening foliar organs (often decompound). Spikelet-bearing axes short racemes; solitary; with very slender rachides (filiform); disarticulating; disarticulating at the joints. Articles not appendaged; disarticulating obliquely (or at least, sub-obliquely); glabrous. Spikelets paired; consistently in long-and-short combinations; in pedicellate/sessile combinations. Pedicels of the pedicellate spikelets free of the rachis. The shorter spikelets female-only. The longer spikelets male-only.
Female-sterile spikelets. The pedicelled spikelets very similar in form to the sessile, but glumes stronger nerved, lemmas slightly shorter, and with 3 functional stamens. The male spikelets with glumes; 2 floreted. The lemmas awnless. Male florets 3 staminate.
Female-fertile spikelets. Spikelets 3–4 mm long; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present (small, glabrous on the back, bearded on sides and front).
Glumes two; more or less equal; long relative to the adjacent lemmas (exceeding them); without conspicuous tufts or rows of hairs; awnless; very dissimilar (both papery, G1 bicarinate, G2 naviculate). Lower glume two-keeled; not pitted; relatively smooth. 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; 0 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; hyaline; not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; awnless; hairless; non-carinate; without a germination flap; 1 nerved. Palea present, or absent (in H. virgatum); when present, conspicuous but relatively short, or very reduced; entire; awnless, without apical setae; not indurated; nerveless. Lodicules present; 2; fleshy; glabrous. Stamens 0 (but with 3 staminodes). Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit small (about 2 mm long in H. virgatum); brown; fusiform; smooth. Hilum short. Embryo large; not waisted.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular, or rectangular and fusiform; having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries triangular. Intercostal short-cells common. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; mostly dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Leaf blade adaxially flat. Midrib conspicuous (via a conspicuous abaxial keel, and a large adaxial bulliform group); with one bundle only, or having a conventional arc of bundles (if two small flanking bundles are regarded as part of the midrib); with colourless mesophyll adaxially, or without colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms not present in discrete, regular adaxial groups (restricted to a single group over the midrib). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the larger bundles); forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 5. 2n = 30.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. 2 species.
Distribution, phytogeography, ecology. Tropical America and Africa.
Mesophytic; species of open habitats; glycophytic. Savanna.
References, etc. Leaf anatomical: based mainly on photos of H. festuciformis supplied by R.P. Ellis, but see also Metcalfe 1960.
Illustrations. • H. virgatum: Nicora & Rúgolo de Agrasar (1987)
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’.