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The grass genera of the world

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

Thelepogon Roth.

Including Rhiniachne Steud.

Habit, vegetative morphology. Rather stout, erect or decumbent annual (often with prop roots). Culms 10–150 cm high; herbaceous; sparsely branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm internodes solid. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades lanceolate (from the amplexicaul base); broad; to 30 mm wide; cordate; flat. Ligule an unfringed membrane, or a fringed membrane; 0.5–0.8 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 sterile (fertile/sterile, but the latter reduced to their pedicels).

Inflorescence. Inflorescence of spicate main branches (of long, brittle golden ‘racemes’); subdigitate (the racemes on a short common axis). Primary inflorescence branches 2–20. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’ (with numerous spikelets). The racemes without spikelets towards the base. Spikelet-bearing axes clustered; with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (curved, concave, compressed below and clavate upwards); without a basal callus-knob; not appendaged; disarticulating transversely; somewhat hairy (i.e., the margins ciliate). Spikelets paired (but the pedicellate one reduced to the pedicel); sessile and pedicellate (the pedicelled component vestigial); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets basally free of the rachis (the pedicel and joint separated below, contiguous above). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets sterile (and vestigial).

Female-sterile spikelets. The pedicellate member absent, represented only the flattened, linear pedicel.

Female-fertile spikelets. Spikelets 5–13 mm long; abaxial; compressed dorsiventrally; falling with the glumes (deciduous with the joint and the sterile pedicel); with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present (annular). Callus short; blunt.

Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; glabrous; pointed; awnless; non-carinate (rounded on the back); very dissimilar (both wingless, more or less rugose, the lower firmer). Lower glume much exceeding the lowest lemma; not two-keeled; convex on the back; not pitted; strongly rugose, or muricate, or tuberculate; 7–9 nerved. Upper glume 1 nerved (to 3?). Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete 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; incised; deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairless (glabrous); much longer than the body of the lemma. Lemmas hairless; non-carinate; without a germination flap; 3 nerved, or 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated (hyaline); 2-nerved; keel-less. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (about 3 mm long); ellipsoid; compressed dorsiventrally. Hilum short. Embryo large (about half the length of the fruit).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (but fairly thin). Microhairs present; panicoid-type; 57–61.5 microns long; 9–10.5 microns wide at the septum. Microhair total length/width at septum 5.4–6.7. Microhair apical cells 33–37.5 microns long. Microhair apical cell/total length ratio 0.55–0.63. Stomata common; 45–51 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (usually); silicified. Intercostal silica bodies crescentic and oryzoid-type. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (pairs, triplets and solitaries). Costal silica bodies ‘panicoid-type’; mainly cross shaped and dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (constituting most of the adaxial epidermis). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’ (but almost so in the midrib). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae. 2 species (T. australiensis, T. elegans).

Distribution, phytogeography, ecology. Tropical Africa, Asia.

Helophytic to mesophytic; species of open habitats; glycophytic. Seasonally wet, heavy soils and disturbed ground.

References, etc. Leaf anatomical: studied by us - T. elegans Roth.

Illustrations. • T. elegans, as Andropogon princeps: Richard, Tentamen Florae Abyssinicae (1851). • General aspect (T. elegans): Gibbs Russell et al., 1990. • T. elegans, 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: 11th December 2017.’.