233. Ambrosia Linnaeus, Sp. Pl. 2: 987. 1753.
豚草属 tun cao shu
Annuals, perennials, or shrubs. Stems erect, decumbent, or prostrate, branched. Leaves usually cauline, opposite throughout or opposite (proximal) and alternate or mostly alternate, sessile or petiolate; blade deltate, elliptic, filiform, lanceolate, linear, obovate, ovate, or rhombic, usually pinnately, sometimes palmately, lobed, both surfaces hairy or glabrate, usually gland-dotted or stipitate glandular, ultimate margin entire or toothed. Capitula discoid, unisexual, female proximal to or intermixed with male, male capitula usually arranged in racemes or spikes; rarely single plants all or mostly male or female. Female capitula: phyllaries 1-8-seriate, outer (1-)5-8 distinct or connate, herbaceous, remainder connate, usually with free tips forming tubercles, spines, or wings; florets 1(-5); corollas 0. Male capitula: involucres cup-shaped to saucer-shaped, 1.5-6 mm in diam.; phyllaries 1-seriate, connate; receptacle flat or convex; paleae spatulate to linear, membranous, sometimes villous, hirtellous, and/or gland-dotted or stipitate glandular, sometimes absent; florets 5-60; corollas whitish or purplish, funnelform, 5-lobed, erect or incurved; staminal filaments connate, anthers free or weakly coherent. Achenes black, ovoid or fusiform, enclosed within globose to obovoid, pyramidal, pyriform, obconical, or fusiform, hard, smooth, tuberculate, spiny, or winged burs; pappus absent. x = 18.
About 43 species: tropical to subtropical and temperate New World, mostly North America; three species (all introduced) in China.
See Payne, J. Arnold Arbor. 45(4): 401-438. 1964.