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Named for C.F. Rottboell.
Including Stegosia Lour.
Excluding Robynsiochloa
Habit, vegetative morphology. Annual; caespitose. Culms 30–300 cm high; herbaceous; branched above. The branching simple. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades broad; flat; without cross venation; persistent. Ligule an unfringed membrane (?), or a fringed 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; overtly heteromorphic (but all similar in texture); in both homogamous and heterogamous combinations (with terminal, homogamous imperfect pairs and heterogamous pairs below). Plants inbreeding; exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence a single raceme, or paniculate (with terete, spike-like ‘racemes’, terminating the culms and branches, or axillary, solitary or in fascicles). Inflorescence axes not ending in spikelets (the upper homogamous spikelet pairs increasingly reduced, forming a tapered, tail-like terminal appendage to the rachis). Rachides hollowed. Inflorescence spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes spikelike (cylindrical, with embedded spikelets); solitary and clustered (fascicled); with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (flattened below, cupular above); with a basal callus-knob; disarticulating transversely, or disarticulating obliquely (and the pedicelled spikelets disarticulating obliquely, leaving shallow crescentic scars); glabrous. Spikelets paired; secund (the sessile spikelets in two alternating rows, on one side of the rachis); all sessile, but recognisably incorporating fused pedicels; 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 spikelets male or sterile, striate, compressed, herbaceous.
Female-fertile spikelets. Spikelets compressed dorsiventrally (trigonous); falling with the glumes (and with the joint, the pedicelled spikelets falling separately). Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; more or less equal; long relative to the adjacent lemmas; awnless; very dissimilar (the lower flat-backed and 2-keeled above, the upper naviculate, winged). Lower glume two-keeled (narrowly winged at the apex); convex on the back to flattened on the back; not pitted; relatively smooth (scabridulous); 11–13 nerved. Upper glume 11–13 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. The proximal incomplete florets male. The proximal lemmas awnless; 3 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; not becoming indurated; entire; entire; awnless; hairless; non-carinate; 3 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated (hyaline); 2-nerved. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm hard; without lipid.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (31–)36–42(–48) microns long; (4.2–)4.5–5.1(–5.4) microns wide at the septum. Microhair total length/width at septum 5.8–9.3. Microhair apical cells (15–)18–24(–29) microns long. Microhair apical cell/total length ratio 0.48–0.57. Stomata common; (22.5–)24–28.5(–30) microns long. Subsidiaries low dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (usually); silicified, or not silicified. Intercostal silica bodies cross-shaped, or vertically elongated-nodular. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS–. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section, or adaxially flat. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (also irregularly grouped); in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Phytochemistry. Leaves without flavonoid sulphates (1 species).
Special diagnostic feature. Lower glume of female-fertile spikelet flattish, not pitted; ‘pedicellate’ spikelets reduced, herbaceous.
Cytology. Chromosome base number, x = 9 and 10. 2n = 20, 36, 40, and 54. 2, 4, and 6 ploid.
Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 4 species.
Distribution, phytogeography, ecology. Tropical and subtropical Africa, Asia.
Commonly adventive. Helophytic to mesophytic; shade species, or species of open habitats; glycophytic. Woodland, swamps, often in disturbed ground or a weed of cultivated ground.
Economic aspects. Significant weed species: R. cochinchinensis.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia microspora and Puccinia levis. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.
References, etc. Morphological/taxonomic: Veldkamp, de Konig and Sosef 1986. Leaf anatomical: Metcalfe 1960.
Illustrations. • Rottboellia purpurascens: Hook. Ic. Pl. 32 (1933). • General aspect of Rottboellia cochinchinensis: Gibbs Russell et al., 1990.
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: 25th January 2024. delta-intkey.com’.
