Plants annual; cespitose. Culms 30-300+ cm, glabrous or sparsely pubescent below the nodes, branching above the bases. Leaves mostly cauline, not aromatic; sheaths sometimes with papillose-based hairs; auricles absent; ligules membranous, ciliate; blades flat. Inflorescences terminal and axillary, solitary rames with more than 1 spikelet unit, spikelets partially embedded in the rame axes; disarticulation in the rame axes. Spikelets heterogamous, in sessile-pedicellate pairs, dorsally compressed, unawned. Sessile spikelets with 2 florets; lower glumes coriaceous, smooth or scabridulous, not pitted, 2-keeled, narrowly winged above; upper glumes coriaceous, 1-keeled, winged; lower florets staminate or sterile; upper florets bisexual; lemmas and paleas hyaline; anthers 3; ovaries glabrous. Pedicels thick, fused to the rame axes. Pedicellate spikelets sterile or staminate; glumes herbaceous. Caryopses with a hard endosperm. x = 9, 10. Named for Christen Friis Rottboell (1727-1797), a Danish botanist.

Rottboellia is a genus of five species, all native to tropical Africa and Asia, represented in all tropical regions of the world by R. cochinchinensis, the species that has been introduced into the Flora region.

1.   Rottboellia cochinchinensis (Lour.) Clayton
Itchgrass

Culms developing prop roots from the lower nodes. Sheaths with 1-3 mm, stiff, papillose-based hairs; ligules 1-1.3 mm, light brown; blades (9)20-50(60) cm long, 10-20(25) mm wide, glabrous abaxially, adaxial surfaces mostly sparsely pubescent, densely pubescent behind the ligules, hairs papillose-based. Rames (3)6-15 cm long, 2-4 mm wide; internodes 6-12 mm. Sessile spikelets: lower glumes 3.5-7 mm long, 1.4-2 mm wide, convex to flat, 11-13(15)-veined, apices bifid; upper glumes 5-6.2 mm, navicular, almost completely enclosing the florets, (13)15-17-veined; anthers of lower florets 2.2-2.3 mm; anthers of upper florets 1.2-2.1 mm; stigmas purple. Pedicels 3-6.5 mm long, 1.5-2.2 mm wide, flat. Pedicellate spikelets 3-8 mm, sterile. Caryopses 3-4 mm long, 2-2.2 mm wide. 2n = 20, 40.

Rottboellia cochinchinensis is a native of southeast Asia. The species is considered one of the world's worst weeds, and is classified as a noxious weed by the U.S. Department of Agriculture. It is established in the southeastern United States, and has been reported from scattered locations elsewhere in the contiguous United States. In Africa, it is controlled by tillage or by fire, followed by shallow, then deep, plowing (Hall and Patterson 1992). Itchgrass aptly describes the effects of the hairs on the skin.