Rottboellia Nov. Gram. Gen. 23 (1779).

Derivation:. Named for Professor C.F.Rottboell, a Danish botanist of the eighteenth century.

Taxonomic revisions, nomenclatural references:. J.F.Veldkamp, Koning and M.S.M.Sosef, Blumea 31: 281–307 (1986).

Key references (keys and floras):. G.Bentham, Flora Australiensis 7: 459–462 (1878), including. Mnesithea in part, and Eremochloa; E.E.Henty, Manual Grasses New Guinea 166 (1969); M.Lazarides, Tropical Grasses S.E. Asia 66–67 (1980); J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 364–365 (1983); B.K.Simon, Key to Australian Grasses 154 (1993); S.W.L.Jacobs and C.A.Wall, Flora of New South Wales 4: 429 (1993); D.Sharp and B.K.Simon, AusGrass (2002); S.W.L.Jacobs, R.D.B.Whalley & D.J.B.Wheeler, Grasses of New South Wales, 4th ed, 361 (2008).

W.D.Clayton & S.A.Renvoize, Genera Graminum (1986), genus (635).

Native. 5 species, from tropical and subtropical Africa, Asia. 1 species in Australia, NT, Qld, and NSW. Also New Guinea and Malesia.

Habit. Annual, tufted. Leaf blades broad. Ligule an unfringed membrane.

Inflorescence. Inflorescence a single raceme or paniculate (with terete, spike-like racemes, terminating the culms and branches, or axillary, solitary or in fascicles), a spatheathe panicle, spatheate, racemes single, not in tight heads, a compound pseudo-inflorescence. Spikelet-bearing axes spikelike (cylindrical, with embedded spikelets), with heteromorphic spikelets (but all similar in texture), solitary and clustered (fascicled), disarticulating at joints. Internodes with a basal callus-knob, disarticulating transversely or disarticulating obliquely (and the pedicelled spikelets disarticulating obliquely, leaving shallow crescentic scars), glabrous.

Spikelets. Spikelets all partially embedded in rachis, dorsally compressed (trigonous), 2 flowered, with 1 fertile floret, paired, all sessile, but recognisably incorporating fused pedicels, in pedicelled/sessile combinations; sessile spikelet with lower incomplete floret. Fertile spikelets falling with glumes (and with the joint, the pedicelled spikelets falling separately).

Glumes. Glumes more or less equal, long relative to adjacent lemmas, awnless, dissimilar (the lower flat-backed and 2-keeled above, the upper naviculate, winged). Lower glume two-keeled (narrowly winged at the apex), convex on back to flattened on back, relatively smooth (scabridulous), 11–13 nerved. Upper glume 11–13 nerved.

Florets. Lower incomplete floret(s) male. Lemmas awnless, 3 nerved, more or less equalling fertile lemmas, similar in texture to fertile lemmas (hyaline), not becoming indurated. Fertile florets 1. Lemmas less firm than glumes, not becoming indurated, entire at apex, entire, muticous, 3 nerved, glabrous. Palea relatively long, entire, 2 nerved. Lodicules 2. Stamens 3. Grain small, compressed dorsiventrally. Hilum short. Embryo large. Pedicels discernible, but fused with rachis. Pedicelled spikelets present, similar in shape to sessile spikelet, sterile.

Kranz Anatomy. C4.

2n = 20, 36, 40, and 54, 2, 4, and 6 ploid, commonly adventive.

Habitat. Helophytic to mesophytic. Woodland, swamps, often in disturbed ground or a weed of cultivated ground. Shade species, or species of open habitats.

Classification. Panicoideae; Andropogoneae.

Notes. Following the treatment of Veldkamp et al. ((1986), Rottboellia is circumscribed to include 5 species. It formerly contained many more species, but these have been placed in other related genera (Glyphochloa, Mnesithea etc). The group is in need of a cladistic study to resolve the taxonomy (B.K.Simon).

Types Species. R. exaltata L.f. (1782) non (L.) L.f. (1779) = R. cochinchinensis (Lour.) Clayton.

Biogeographic Element. Clifford & Simon 1981, Simon & Jacobs 1990: Old World Tropics.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith