212. Tridax Linnaeus, Sp. Pl. 2: 900. 1753.
羽芒菊属 yu mang ju shu
Herbs, annual or perennial. Leaves opposite, petiolate or sessile; blade deltate, lanceolate, lanceolate-ovate, or ovate, often pinnately or palmately lobed, both surfaces glabrate, hirsute, scaberulose, or strigillose, ultimate margin coarsely toothed to subentire. Synflorescence of solitary capitula or cymose. Capitula radiate or discoid; involucres cylindric to hemispheric, 4-8 mm in diam.; phyllaries persistent, in 2 or 3+ series, outer usually shorter, more herbaceous, inner often scarious; receptacle convex to conical; paleae persistent, lanceolate-linear, scarious, weakly conduplicate, often apically toothed. Ray florets female, fertile; lamina pale yellow, white, or purplish. Disk florets bisexual, fertile; corollas yellowish, whitish, or purplish, tubes shorter than cylindric or funnelform throats, lobes 5, usually deltate, sometimes corollas of marginal florets bilabiate. Achenes obconical to obpyramidal, 3-5-angled, densely pilose-sericeous, glabrous, or villous; pappus persistent, of plumose or ciliate, setiform scales or bristles, rarely absent. x = 10.
About 26 species: tropical America and Asia; one species (introduced) in China.
See Powell, Brittonia 17(1): 47-96. 1965.