Mant. Pl., 157, 286. 1771.
Annuals or perennials, 10–50(–70+) cm. Stems erect or decumbent, branched from bases and/or distally (sometimes rooting at proximal nodes). Leaves cauline; opposite; petiolate or sessile; blades (1- or 3-nerved) lanceolate to lance-linear, bases cuneate, margins serrate to subentire, faces sparsely scabrellous. Heads radiate, in loose, corymbiform arrays or borne singly. Involucres hemispheric, 3–5 mm diam. Phyllaries persistent, 8–12+ in 2–3 series (lanceolate to linear, subequal, thin-herbaceous, spreading in fruit). Receptacles flat to convex, paleate (paleae linear to filiform, not conduplicate, falling with fruits). Ray florets 20–40 (in 2–3+ series), pistillate, fertile; corollas white or whitish. Disc florets 15–30+, bisexual, fertile; corollas white or whitish, tubes much shorter than ampliate, cylindric throats, lobes 4–5, ± deltate. Cypselae obcompressed, weakly 3–4-angled (not winged, epidermes usually corky and rugose to tuberculate); pappi persistent, coroniform (sometimes with 2 teeth). x = 11.
Mostly warm-temperate to tropical New World, introduced in Old World.
Species 1–4 (1 in the flora).