The grass genera of the world

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

Heteropholis C.E. Hubb.

~ Mnesithea

Habit, vegetative morphology. Annual, or perennial; mostly decumbent. Culms slender, 60–170 cm high; herbaceous; sparsely to amply branched above, or unbranched above. The branching simple. Culm internodes solid. Leaves not basally aggregated; auriculate (with sheath auricles), or non-auriculate. Leaf blades linear to lanceolate; broad, or narrow; cordate, or not cordate, not sagittate; flat, or folded (conduplicate when young, later flat); without cross venation. Ligule an unfringed membrane.

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 male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic; all in heterogamous combinations.

Inflorescence. Inflorescence of single, cylindrical to flattened, dorsiventral ‘racemes’ terminating culms and branches. Rachides hollowed (with small cavities). Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs (the ‘racemes’ spatheate). Spikelet-bearing axes spikelike (the spikelets apparently opposite, by fusion of joints and pedicels); solitary; with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (clavate, with 2 small cavities); with a basal callus-knob; not appendaged; disarticulating transversely; glabrous. Spikelets paired; secund (dorsiventral ‘racemes’); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.

Female-sterile spikelets. The pedicelled spikelet thinly leathery, the G1 not lacunose. The male spikelets with glumes. The lemmas awnless.

Female-fertile spikelets. Spikelets abaxial; compressed dorsiventrally; falling with the glumes (and with the joint). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; glabrous; awnless; G2 one-keeled, often obscurely so; very dissimilar (the G1 leathery, transversely rugose or pitted and with two keel-wings above, the G2 smooth, membranous, more or less naviculate). Lower glume not two-keeled (winged only at the tip); convex on the back; not pitted; lacunose with deep depressions, or rugose (transversely); 7–9 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate, or epaleate. Palea of the proximal incomplete florets when present, reduced. The proximal incomplete florets male, or sterile. 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; 0 nerved, or 3 nerved. Palea present; relatively long, or conspicuous but relatively short, or very reduced; entire; awnless, without apical setae; not indurated (hyaline); 2-nerved, or nerveless; keel-less. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less panicoid-type (but relatively broad); 52.5–72 microns long; 6–9 microns wide at the septum. Microhair total length/width at septum 7–10. Microhair apical cells 30–45 microns long. Microhair apical cell/total length ratio 0.57–0.63. Stomata common; 43.5–46.5 microns long. Subsidiaries triangular (with tall points). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified (sometimes). Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, dumb-bell shaped, and nodular.

Transverse section of leaf blade, physiology. C4; XyMS–. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (a large keel bundle, with several smaller laterals); with colourless mesophyll adaxially. Bulliforms not present in discrete, regular adaxial groups (the adaxial epidermis mainly bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (each primary bundle). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 5 species.

Distribution, phytogeography, ecology. Tropical Africa, Asia, Australia.

In wooded grassland.

References, etc. Morphological/taxonomic: Hubbard 1956. Leaf anatomical: studied by us - H. nigrescens (Yhw.) C.E. Hubb.

Illustrations. • H. benoistii, H. nigrescens and H. sulcata, sessile spikelets: Koning, Sosef & Veldkamp, Gard. Bull. Singapore 36 (1983)

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.’.