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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Hypogynium Nees

~ Andropogon

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)


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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’.

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