Annual herbs, large, branching, coarse, sometimes spiny. Leaves alternate, lobed or coarsely dentate, petiolate. Heads discoid, rather small, greenish, unisexual. Staminate heads densely aggregated, terminal, globose; involucral bracts distinct, spreading, 1-3-seriate, oblong lanceolate; receptacle cylindric, paleaceous; corollas tubular, 5-toothed, filaments and anthers free, mucronate at apex, obtuse at base; style clavate at apex, undivided. Pistillate heads ovoid or oblong, fasciculate in leaf axils; outer series of involucral bracts oblong-lanceolate, spreading, small, inner bracts forming an ellipsoid or ovoid, sharply prickly 2-beaked utricle enclosing 2 florets; corolla absent; pappus none; style 2-cleft, branches filiform, exserted. Achenes 2 per head, oblong, enclosed within utricle.
A genus primarily or wholly American, with several weedy species now dispersed into almost every temperate and tropical inhabited region; one species in Taiwan.
Löve, D. & P. Dansereau. 1959. Biosystematic studies on Xanthium: Taxonomic appraisal and ecological status. Canad. J. Bot. 38: 173-208. 1959.
McVaugh, R. 1984. Flora Nova-Galiciana. Vol. 12. Compositae. The University of Michigan Press, Ann Arbor, pp. 1092-1095.
