Rottboellia sp.

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.)

Generic Description
Plants annual herbs; culms erect; internodes solid.  Leaf sheaths with spreading, rigid hairs; auricles absent; ligule a hairy membrane; blades long and flat, the blades nearest the inflorescence reduced.  Inflorescence a spike-like raceme, cylindrical, disarticulating into floral units which consist of a fertile sessile spikelet, pedicellate spikelet, and internode; internode swollen, hollow, enlarged at the apex, glabrous, the lower spikelet embedded in the internode; callus truncate and peg-like; pedicel shorter but otherwise similar to and fused to the internode.  Spikelets paired, heteromorphic, awnless, abaxial, dorsa-ventrally compressed.  First glume of sessile spikelet many-nerved, smooth to muricate, indurate, with inrolled margins; second glume many-nerved, boat-shaped, closely following the outline of the internode; lower floret staminate, the lower lemma mambranous to chartaceous, the lower palea well-developed; upper floret perfect, with lemma hyaline and awnless, the stigmas purple, the caryopsis ovate.  Pedicellate spikelet sterile and green; the first glume many-nerved, with scabrous and inrolled margins and usually cleft apex.

Explanatory Notes
Rottboellia is a small genus of about four species native to the tropics of the Old World.  It is a typical member of the grass tribe Andropogoneae, which is characterized by the inflorescence disarticulating into floral units consisting of a sessile spikelets, pedicellate spikelet, and internode.  Some closely related genera include Manisuris, Coelorachis, and Hemarthria.  Diagnostic features of Rottboellia include the racemose inflorescence, a pedicel fused to the swollen floral internode, and heterotropic and awnless spikelets.  One species of the genus Rottboellia cochinchinensis, is presently included on the list of weeds for the Federal Noxious Weed Act.

Species Name: Rottboellia cochinchinensis (Lour.) Clayton, Kew Bull. 35: 817. 1981.

Synonyms
Rottboellia exaltata auct., non. (L.) L.f. 1779.
Stegosia cochinchensis Lour., Fl. Cochinch. 51. 1790.
Manisuris exaltata Kuntze, Rev. Gen. Pl. 2:779. 1891.
Stegosia exaltata Nash, N. Am. Fl. 17:84. 1909.

Common Names
A list of common names of Rottboellia cochinchinensis (as R. exaltata) has been compiled by Holm et al. (1977).  This list has been incorporated into the following list: Kokoma grass (Australia); sancarana (Cuba); guinea-fowl grass (Eastern Africa); barsali, bura swooate, dholu, konda panookoo (India?); bandjangan, djoekoet kikisian (Indonesia); rice grass (Jamaica); aguingay, annarai, bukal, gaho, girum, nagei, sagisi (Philippines); guineafowl grass, kokomo grass, shamva grass (Rhodesia); corn grass (Trinidad); itchgrass, Raoul grass (United States); paja peluda (Venezuela); jointed grass, mulungwe, shamwa grass (Zambia).

Description
Annual grasses; inflorescence a jointed, cylindrical raceme 3-15 cm long; floral units consisting of a sessile spikelet, pedicellata spikelet, and internode; pedicel fused to the swollen floral internode; spikelets awnless, 3.5-6 mm long, 2.5-3 mm wide.

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.

Distribution
A native of the Old World tropics, widespread in tropical Asia and the Pacific Islands.  The species has been introduced into tropical America and now occurs in Central and northern South America, throughout the Caribbean, and in Florida and Louisiana in the United States.  It has also spread into Australia and much of Africa.

Figure
Rottboellia cochinchinensis.  A.  Lower portion of culm, showing annual nature (with inset showing solid stem) (0.75x);  B.  Upper portion of culm, showing pubsecence and spikelike raceme (0.75x); C.  Sheath/blade joint, showing ligule (4.5x); D.  Young flowering branch (0.75x); E.  Top portion of inflorescence (1.5x); F.  Floral unit (sessile spikelet, pedicellate spikelet, and internode (9x).

Source: Williams 2623, Philippines (NY).

Economic Impact
Rottboellia cochinchinensis is an aggressive weed under various ecological conditions.  In some areas, it seems to prefer wet, coarse-textured soils at the lower altitudes, sometimes even growing in shallow water.  In other areas it is prominant in open, well-drained places at higher altitudes, and is one of the important species in old field succession.  In the Americas it is an aggressive weed of sugarcane fields.  In Africa and Malayasia it causes severe crop damage to corn, cotton, peanut, soybean, and sugarcane.  Thomas (1970) reported the species in Rhodesia only in heavier soils--clay to sandy clay loams--the type of soil in Louisiana sugarcane growing areas, where the weed is becoming more of a problem each year.

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).

Explanatory Notes
The name Rottboellia exaltata has been misapplied and this nomemclatural problem was reviewed by Clayton (1980, 1981).  The correct name for this widespread species is Rottboellia cochinchinensis (Lour.) Clayton.  However, Simon (1982--Taxon 564-573) has formally proposed to conserve the name Rottboellia exaltata L.f.

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).

Literature Cited
Agati, J. and C. Calica.  1949.  The leaf-gall disease of rice and corn in the Philippines. Phil. J. Agr. 14:31-38.

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.