Decumbent to erect annual herbs. Leaves petiolate or sessile, opposite with entire or dentate margins. Capitula hemispherical, radiate, 1(–3) in leaf axils or branch forks; involucral bracts 10–13, 2-seriate; outer series herbaceous, persistent; inner series enveloping ray florets, becoming hardened and enlarged at fruiting and shed with cypselas; receptacle convex, with membranous scales. Ray florets 1-seriate, female, yellowish; disc florets functionally male, tubular, corolla funnel-shaped or campanulate, 5-lobed, yellowish; styles hispidulous with filiform branches; anthers sagittate at base. Cypselas enclosed within bracts, entire accessory fruit ellipsoid, fusiform or compressed and cuneate, prickly; pappus absent.
6 species native to the New World; 2 species introduced in Australia.