The grass genera of the world
Habit, vegetative morphology. Stoloniferous. Culms 100–150 cm high; herbaceous (erect); branched above. Culm nodes exposed; hairy. Culm leaves present. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Sheaths with tuberculate hairs. Leaf blades linear; narrow; 4–6 mm wide; flat (rarely), or folded; without cross venation; persistent. Ligule an unfringed membrane; somewhat truncate; 1.5–2 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 (and the sessile female spikelets crustaceous, the pedicellate males herbaceous); all in heterogamous combinations.
Inflorescence. Inflorescence a solitary raceme terminating the culm; espatheate; not comprising partial inflorescences and foliar organs (the raceme more or less disengaging from the uppermost, non-spathiform sheath). Spikelet-bearing axes racemes (spiciform), or spikelike; the spikelet-bearing axes with more than 10 spikelet-bearing articles (15 to 20); solitary; with substantial rachides; disarticulating; disarticulating at the joints. Articles non-linear; with a basal callus-knob; not appendaged; disarticulating obliquely; glabrous. Spikelets paired; secund (the raceme strongly dorsiventral, the sessile spikelets in two alternating rows on one side of the rachis); sessile and pedicellate; consistently in long-and-short combinations; in pedicellate/sessile combinations. Pedicels of the pedicellate spikelets discernible, but fused with the rachis (to a variable extent). The shorter spikelets hermaphrodite. The longer spikelets male-only.
Female-sterile spikelets. Pedicellate spikelets herbaceous, asymmetrically lanceolate; florets 1–2, the lower male, the upper male or sterile. The male spikelets with glumes; with proximal incomplete florets, or without proximal incomplete florets; 1 floreted, or 2 floreted. The lemmas awnless. Male florets 3 staminate.
Female-fertile spikelets. Spikelets 6 mm long; orange; abaxial; compressed dorsiventrally (thick, obconical); planoconvex; falling with the glumes (and the pedicel and rachis segment); not disarticulating between the florets; with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus short; blunt (dumpy).
Glumes two; more or less equal; long relative to the adjacent lemmas; free; dorsiventral to the rachis; hairless; glabrous; not pointed (G1 bidentate, G2 blunt); awnless; very dissimilar (G1 crustaceous and rounded on the back, G2 leathery on the back with hyaline margins, naviculate and keel-winged above). Lower glume two-keeled (the keels winged above); convex on the back; not pitted; muricate (shining between the tiny projections); about 17 nerved. Upper glume about 15 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed (indurated below, with hyaline wings). The proximal incomplete florets male. The proximal lemmas ovate-lanceolate; awnless; 3 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (membranous); not becoming indurated; entire; pointed; awnless; hairless; glabrous; carinate (conspicuously naviculate); without a germination flap. Palea present; relatively long (linear); entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (the margins narrow, inflexed); 2-keeled. Palea back glabrous. Palea keels wingless; glabrous. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Ovary apically glabrous. Styles free to their bases; free. Style bases adjacent. Stigmas 2.
Fruit, embryo and seedling. Fruit small; golden yellow; subglobose; not noticeably compressed; glabrous. Hilum short. Embryo large. Endosperm hard; containing only simple starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower, more regularly rectangular); of similar wall thickness costally and intercostally (the walls of medium thickness). Intercostal zones with typical long-cells. Mid-intercostal long-cells rectangular to fusiform; having markedly sinuous walls to having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries non-papillate; rather consistently triangular. Guard-cells overlapping to flush with the interstomatals (consistently very slightly overlapping them). Intercostal short-cells common; in cork/silica-cell pairs and not paired (often solitary); silicified. Intercostal silica bodies tall-and-narrow, cross-shaped, and oryzoid-type. Neither macrohairs no prickles seen. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; panicoid-type; cross shaped to dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath extensions absent. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (with one large median); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in places), or not present in discrete, regular adaxial groups (for the most part, the epidermis more or less irregularly bulliform); occasionally in simple fans (of the Zea type). Combined sclerenchyma girders present (with all the primaries and some of the other main bundles, some others with abaxial girders only). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae (?); Rottboelliinae (?). 1 species.
Distribution, phytogeography, ecology. Tropical Africa.
References, etc. Leaf anatomical: this project.
Illustrations. • R. purpurascens: Jacques-Félix, 1962
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: 13th November 2017. delta-intkey.com/grass’.