Rottboellia L.f.
Named for C.F. Rottboell.
Including Stegosia Lour.
Excluding Robynsiochloa
Habit, vegetative morphology. Annual; caespitose. Culms 30–300 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades broad; flat; without cross venation; persistent; an unfringed membrane (?), or a fringed membrane.
Reproductive organization. Plants bisexual, 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 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.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae.
Distribution, ecology, phytogeography. 4 species; 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.
Holarctic, Paleotropical, Neotropical, and Australian. Tethyan. African, Madagascan, Indomalesian, and Neocaledonian. Macaronesian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, Malesian, and Papuan. Caribbean, Pampas, and Andean. North and East Australian. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia microspora and Puccinia levis. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.
Economic importance. Significant weed species: R. cochinchinensis, R. exaltata.
References, etc. Morphological/taxonomic: Veldkamp, de Konig and Sosef 1986. Leaf anatomical: Metcalfe 1960 and this project.
Illustrations. • General aspect. • Inflorescence detail. • Disarticulated inflorescence ‘joint’. Rottboellia exaltata. Sessile spikelet (left), pedicellate spikelet with its pedicel fused with the rachis (right), and basal elaiosome.
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).
