The grass genera of the world

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

Hyperthelia W. Clayton

~ Hyparrhenia (including H. dissoluta)

Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 100–750 cm high; herbaceous; to 1 cm in diameter; branched above (to form compound inflorescences). Culm nodes glabrous. Culm internodes hollow. Young shoots intravaginal. The shoots not aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades linear; broad, or narrow; 3–40 mm wide; flat, or rolled (on drying); pseudopetiolate (pseudopetioles to 16 cm long), or not pseudopetiolate; without cross venation; persistent. Ligule an unfringed membrane (usually), or a fringed membrane (rarely); truncate, or not truncate (rounded to acute, the upper edges of the sheath adnate to its sides); 3–4 mm long. Contra-ligule 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. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic; in both homogamous and heterogamous combinations (with one homogamous pair, at the base of the lower raceme).

Inflorescence. Inflorescence falsely paniculate (large, leafy); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes very much reduced (usually), or ‘racemes’ (rarely); the spikelet-bearing axes usually with only one spikelet-bearing ‘article’ (rarely with 4 or 5); paired (the pair subtended by a linear to lanceolate spatheole, the bases terete, sometimes deflexed); with very slender rachides; disarticulating; disarticulating at the joints. ‘Articles’ linear; appendaged (the raceme-base with a long scarious appendage at the tip, 3–20 mm long, flat or rolled into a funnel around the raceme base); disarticulating obliquely. Spikelets paired, or in triplets (sometimes having one female-fertile spikelet with a pair of pedicelled male spikelets, the triplet disarticulating in its entirety); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite (in the heterogamous combinations), or male-only (in the homogamous combinations). The ‘longer’ spikelets male-only.

Female-sterile spikelets. The homogamous and pedicellate spikelets male, linear-lanceolate, with two hyaline lemmas; pedicellate spikelets with a short basal callus. The male spikelets 2 floreted.

Female-fertile spikelets. Spikelets 8–35 mm long; abaxial; not noticeably compressed to compressed dorsiventrally; biconvex; falling with the glumes; not disarticulating between the florets; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long; pointed.

Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; dorsiventral to the rachis; hairy (G1, towards the tip), or hairless (G2); without conspicuous tufts or rows of hairs; not pointed (G1 bifurcate, G2 blunt); awned (G2, sometimes), or awnless; non-carinate; very dissimilar. Lower glume much exceeding the lowest lemma; not two-keeled; sulcate on the back; not pitted; relatively smooth. Upper glume 1 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; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline at margins and tips); becoming indurated along a central sulcate column below the awn; incised; shortly 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairy; much longer than the body of the lemma. Lemmas hairless (or with a few hairs only, at the edges); non-carinate (flat, sulcate); without a germination flap; 1 nerved. Palea present, or absent; when present, conspicuous but relatively short, or very reduced. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 3–4 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; dark red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; narrowly ellipsoid. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Stomata common. Subsidiaries dome-shaped and triangular. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR cell chloroplasts centrifugal/peripheral. Mesophyll without adaxial palisade. Leaf blade adaxially flat (practically smooth). Midrib conspicuous; having complex vascularization. Bulliforms somtimes present in discrete, regular adaxial groups (but mostly in irregular groups); sometimes in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with most large bundles).

Special diagnostic feature. Spikelets in much-reduced andropogonoid ‘racemes’, each of the latter reduced to a single triplet and enclosed at its base by a trumpet-like development of the peduncle tip (sometimes), or not borne as in ‘Anadelphia scyphofera’ (q.v.).

Cytology. Chromosome base number, x = 10.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 6 species.

Distribution, phytogeography, ecology. Tropical and southern Africa.

Mesophytic; species of open habitats; glycophytic. Grasslands and savanna.

Economic aspects. Grain crop species: Hyperthelia edulis harvested wild.

References, etc. Morphological/taxonomic: Clayton 1966. Leaf anatomical: studied by us - H. dissoluta (Steud.) Clayton.

Illustrations. • H. dissoluta, as Andropogon ruprechtii: Wood, Natal Plants 2 (1904). • General aspect (H. dissoluta): Gibbs Russell et al., 1990

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.’.