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Contributed by: Dr. Robert D. Webster; Research School of Biological Sciences; The Australian National University; Canberra City, A.C.T. 2601; Australia. U.S. Department of Agriculture APHIS-PPQ. Noxious weeds of the Federal Noxious Weed Act, No. 37
Family Name: Poaceae [Gramineae]
Genus Name: Rottboellia L.f., Nov. Gram. Gen. 23. 1779., nom. cons. Type species: Rottboellia exaltata auct., non (L.) L.f. 1779. (= Rottboellia cochinchinensis (Lour.) Clayton, Kew Bull. 35:817. 1981.)
Species Name: Rottboellia cochinchinensis (Lour.) Clayton, Kew Bull. 35: 817. 1981.
Plants tall annuals, frequently with prop-roots; flowering culms 5-30 dm tall, branched, mostly 5- to 10-noded; nodes glabrous; internodes glabrous, grooved, ribbed, solid to spongy. Leaf sheaths keeled to rounded, distinctly ribbed, smooth, usually covered with stiff, irritating, papillose-based, setaceous hairs, the upper sheaths hairy or glabrous, without auricles; ligule a hair-fringed membrane 1-2 mm long, truncate; blades not distinctly distichous, flat, keeled, mostly 25-40 cm long, 5-25 mm broad, linear, acuminate, base cordate, hairy or glabrous, scabrous, margins scabrous; prophyllum with pronounced scabrous wings. Inflorescence a jointed raceme, 3-15 cm long, cylindrical, the upper spikelets becoming reduced, disarticulating into floral united which consist of a sessile spikelet, pedicellate spikelet, and internode; internode minutely muricate, 5-8 mm long, deeply grooved on the lower part, apex hollow; callus soft, smooth, truncate and peg-like; pedicel similar in appearance and fused to the internode, but shorter 3-5 mm long. Sessile spikelet embedded in the internode, 3.5-6 mm long, 2.5-3 mm wide; first glume as long as the spikelet, oblong to lanceolate, 9- to 11-nerved, rounded to cleft, indurate, convex, muricate, glabrous, slightly winged at the apex, margins inrolled; second glume many-nerved, keeled on the upper part, boat-shaped, smooth on the lower part and muricate upwards, indurate to cartilaginous, following the outline of the internode; lower lemma oblong to lanceolate, faintly 3-nerved, as long as the second glume, membranous to chartaceous; lower palea well-developed and similar to the lemma; upper floret perfect, hyaline. Caryopsis oblong, 3-4 mm long.
Source: Williams 2623, Philippines (NY).
The species is presently most destructive in eastern Afrcia, the Philippines, and along the shores and islands of the Gulf of Mexico and the Caribbean area. See Holm et al. (1977) for a detailed list of countries where Rottboellia cochinchinensis is a serious problem, and the crops involved.
The common name "itchgrass" is derived from the presence of rigid penetrating hairs on the leaf sheaths. Although attempts have been made to use the plant for pasture in many areas, these hairs will break off in flesh and cause severe irritation, making the species a poor fodder.
Rottboellia cochinchinensis is an alternate host of the virsuses causing corn leaf gall and rice leaf gall (Agati and Calica 1949).
Diagnostic features useful in distinguishing this species from other members of the genus include sharp irritating hairs on the leaf sheaths, the length of the spike-like raceme (3-15 cm long), and spikelet length (3.5-6 mm long).
Clayton, W.D. 1980. Proposal to conserve Rottboellia L.f. 1781 against Rottboellia L.f. 1779. Taxon 29:692.
. 1981. Notes on the tribe Andropogoneae (Gramineae). Kew Bull. 35:817.
Holm, L.G., D.L. Plucknett, J.V. Pancho, and J.P. Herberger. 1977. The world's worst weeds: Distribution and biology. University Press of Hawaii, Honolulu. 609 pp.
Thomas, P. 1970. A survey of the weeds of arable lands in Rhodesia. Rhod. Agr. J. 67(2):34-37.
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Last updated on Wednesday, November 05, 2003 at 01:31 PM
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