232. Xanthium Linnaeus, Sp. Pl. 2: 987. 1753.
苍耳属 cang er shu
Annuals. Stems erect, branched. Leaves cauline, mostly alternate (proximal 2-6 sometimes opposite), petiolate; blade lanceolate, linear, ovate, orbicular-deltate, or suborbicular, often palmately or pinnately lobed, both surfaces hirtellous or ± strigose, usually gland-dotted as well, ultimate margin entire or ± toothed. Capitula discoid, either female (proximal) or functionally male (distal), in racemiform to spiciform arrays or borne singly (in axils). Female capitula: involucres ± ellipsoid, 2-5 mm in diam. at anthesis; phyllaries in 6-12 series, outer 5-8 distinct, remainder (sometimes interpreted as paleae) proximally connate, their distinct tips mostly ± hooked (distal 1-3 usually longer, stouter, and not hooked), whole becoming a hard, prickly perigynium (a bur); florets 2, corollas 0. Male capitula: involucres saucer-shaped, 3-5 mm in diam.; phyllaries in 1 or 2 series, distinct to bases; receptacle conical to columnar; paleae spatulate to cuneiform or linear, membranous, apically villous or hirtellous; florets 20-50, corollas whitish, funnelform, lobes 5, erect or reflexed; filaments connate, anthers free or weakly coherent. Achenes black, fusiform, enclosed in obovoid to ellipsoid, hard, prickly, 2-chambered burs; pappus absent. x = 18.
Two or three species: New World, introduced nearly worldwide; two species (both introduced) in China.
For more on the genus, see Widder (Repert. Spec. Nov. Regni Veg. Beih. 20: 1-222. 1923; Phyton (Horn) 11: 69-82. 1964), Löve and Dansereau (Canad. J. Bot. 37: 172-208. 1959), and Löve (Lagascalia 5: 55-71. 1975).