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The grass genera of the world

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

Rhytachne Desv.

Including Lepturopsis Steud.

Habit, vegetative morphology. Annual (rarely), or perennial; caespitose. Culms 25–120 cm high; herbaceous; branched above (R. gonzalezii), or unbranched above. The branching simple. Culms few noded. Culm nodes glabrous. Culm internodes solid. Young shoots intravaginal. Leaves not basally aggregated; auriculate (from the apex of the sheath), or non-auriculate (but with long hairs in the auricular position). Leaf blades linear; narrow (to filiform); 1–9 mm wide; setaceous to not setaceous (often rolled); flat, or folded, or rolled, or acicular; without cross venation; persistent. Ligule an unfringed membrane; truncate; 0.75–2 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets nearly always of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic (the pedicellate spikelets nearly always much reduced); all in heterogamous combinations.

Inflorescence. Inflorescence a single raceme (of single, usually terminal ‘racemes’ these cylindrical and themselves culm-like until the embedded spikelets open). Rachides hollowed (the articles hollowed to take the contiguous sessile spikelets). Inflorescence spatheate, or espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikelike; the spikelet-bearing axes with more than 10 spikelet-bearing ‘articles’ (12–30); solitary; with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (clavate, as long as or longer than the sessile spikelet); with a basal callus-knob; appendaged, or not appendaged (the summit of the joint concave to cupular); disarticulating transversely; somewhat hairy (at the apex and onto the pedicels), or glabrous. Spikelets paired (but the pedicellate member sometimes reduced to a sclae-tipped pedicel); secund (the ‘racemes’ somewhat dorsiventral, the sessile spikelets in two alternating rows on one side); sessile and subsessile, or sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile (variously reduced, sometimes suppressed), or hermaphrodite (R. perfecta).

Female-sterile spikelets. The pedicelled member usually suppressed, vestigial or represented by an awn, occasionally well developed (even bisexual, in R. perfecta). The pedicel usually foliaceous.

Female-fertile spikelets. Spikelets 2–8 mm long; abaxial; compressed dorsiventrally; planoconvex, or biconvex; falling with the glumes; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present, or absent. Callus absent, or short; blunt.

Glumes two; more or less equal; about equalling the spikelets; long relative to the adjacent lemmas (exceeding them); dorsiventral to the rachis; hairless; glabrous; pointed; awned (G1 and/or G2, sometimes), or awnless; non-carinate; very dissimilar (G1 leathery, convex, often transversely rugulose, G2 membranous or hyaline, with or without a terminal subule). Lower glume two-keeled (and sometimes obscurely winged), or not two-keeled (then the sides rounded); convex on the back; not pitted; relatively smooth, or rugose (or longitudinally ribbed); obscurely 5 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 reduced. The proximal incomplete florets male, or sterile (rarely). The proximal lemmas awnless; 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 linear-lanceolate to oblong; less firm than the glumes (hyaline); not becoming indurated; entire; awnless; hairless; non-carinate; without a germination flap; 1–2 nerved (rarely 3). Palea present; relatively long, or conspicuous but relatively short, or very reduced (shorter than the lemma, or very short); entire; awnless, without apical setae; textured like the lemma; not indurated (hyaline); 2-nerved, or nerveless; keel-less. Lodicules present; 2; free; fleshy. Stamens 3. Anthers 1.5–2.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Stigmas 2; brown.

Fruit, embryo and seedling. Fruit compressed dorsiventrally.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or lacking. Papillae absent. Long-cells similar in shape costally and intercostally, or markedly different in shape costally and intercostally (with the costals much smaller); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present, or absent; when present, panicoid-type. Stomata common, or absent or very rare. Subsidiaries triangular. Intercostal short-cells common; in cork/silica-cell pairs (abundant); silicified. Intercostal silica bodies rounded (to elliptical). Costal short-cells predominantly paired. Costal silica bodies rounded; not sharp-pointed.

Transverse section of leaf blade, physiology. Leaf blades consisting of midrib, or ‘laminar’.

C4; XyMS– (seemingly). PCR cell chloroplasts centrifugal/peripheral. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section, or adaxially flat. Midrib conspicuous (or the blade acicular and reduced to the midrib); having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (typical bulliforms sometimes absent, the epidermis of large cells); sometimes in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Spikelets not arranged as in Manisuris (q.v.).

Cytology. 2n = 20.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 12 species.

Distribution, phytogeography, ecology. Tropical and southern Africa, Madagascar, tropical South America.

African and Madagascan.

Helophytic (pans and riversides), or mesophytic (grasslands); species of open habitats; glycophytic.

Rusts and smuts. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Tolyposporella.

References, etc. Morphological/taxonomic: Clayton 1978. Leaf anatomical: Metcalfe 1960.

Special comments. Fruit data wanting. Illustrations. • R. gracilis: Hook. Ic. Pl. 31 (1922). • General aspect (R. robusta): Gibbs Russell et al., 1990. • R. rottboellioides (as Rottboellia loricata): Lamson-Scribner (1890). • R. subgibbosa: 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.’.