Annuals and perennials, mostly 20-120 cm. Stems often decumbent (rooting at proximal nodes), sparsely to densely branched. Leaves cauline; all or mostly opposite; petiolate; blades mostly 1-nerved, deltate to ovate, or elliptic to lanceolate, margins entire or toothed, faces glabrous or ± pilose, puberulent, or strigoso-hispid, sometimes gland-dotted. Heads discoid, in dense to open, cymiform to corymbiform arrays. Involucres campanulate, 3-6 mm. Phyllaries persistent, 30-40 in 2-3 series, usually 2-nerved, lanceolate, ± equal (often indurate, margins scarious). Receptacles conic, epaleate [paleate]. Florets 20-125; corollas white or bluish to lavender, throats ± campanulate (lengths 2 times diams.); styles: bases not enlarged, glabrous, branches ± linear to clavate (usually papillose and dilated distally). Cypselae prismatic, 4-5-ribbed, glabrous or sparsely strigoso-hispidulous; pappi persistent, of 5-6 aristate scales, or coroniform, or 0. x = 10.