Tridax 長柄菊屬
型態特徵
Annual or perennial herbs. Leaves opposite, incised-toothed or pinnatisect, segments narrow. Heads long peduncled, heterogamous, radiate. Ray florets few, fertile, corolla with a slender glabrous tube and broad yellow or pale ligule, or 2-lipped with outer lip large, 3-lobed and inner lip small, 2-lobed or unlobed. Disc florets bisexual, fertile; corolla tube narrowly funnelform, tube short, limb elongate, 5-lobed. Involucre ovoid to campanulate; bracts various, inner ones broader than outer. Receptacle flat or concave, paleae membranaceous. Anthers linear, base short auriculate. Style branches of disc florets hairy apically, tips subulate. Achenes turbinate or oblong, much shorter than corolla. Pappus of many short or long, aristate, feathery bristles.
About 30 species in tropical America; one species introduced into tropical Asia and naturalized in Taiwan.
