Rhytachne Desv.
Including Lepturopsis Steud.
Habit, vegetative morphology. Annual (rarely), or perennial; caespitose. Culms 25–120 cm high; herbaceous; unbranched above; 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; an unfringed membrane; truncate; 0.75–2 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, 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); spikelet-bearing axes 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 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.
Cytology. 2n = 20.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae.
Distribution, ecology, phytogeography. 12 species; tropical and southern Africa, Madagascar, tropical South America. Helophytic (pans and riversides), or mesophytic (grasslands); species of open habitats; glycophytic.
Paleotropical. African and Madagascan. Sudano-Angolan and West African Rainforest. Somalo-Ethiopian and South Tropical African.
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. • General aspect
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
