Description from Flora of China
Herbs, annual or perennial, erect, branched, strigose. Leaves opposite, toothed. Capitula terminal on stems and branches or axillary, pedunculate, heterogamous; involucre campanulate; phyllaries imbricate, ca. 2-seriate; receptacle flat or convex, paleaceous; paleae awnlike. Ray florets bisexual, mostly fertile, lamina minutely 2-lobed, white to yellowish. Disk florets bisexual, corolla tubular, greenish white to yellowish, 4- or rarely 5-lobed; anthers entire or very shortly bifid at base; style branches obtuse, mammillate at apex. Achenes thick, maturing and falling rapidly, those of ray florets 3-angled, those of disk florets compressed, 4-angled, coarsely hairy, tuberculate, margin with 1-3 minute teeth, apex truncate and depressed; pappus absent, coroniform, or of 2 or 3 awns. x = 11.
About five species: mostly warm-temperate to tropical New World, introduced in Old World; one species (introduced) in China.