Perennials, 50-200 cm (usually rhizomatous, colonial, rhizomes relatively slender). Stems erect to decumbent (sometimes rooting at proximal nodes), not much branched distal to bases. Leaves cauline; opposite; petiolate; blades usually 3-nerved from bases, deltate, oblanceolate, ovate, ovate-deltate, oblong, or triangular, margins dentate or lobed (to dissected in C. dissectum), faces glabrate to puberulous, villosulous, or hispidulous, gland-dotted. Heads discoid, in tight, corymbiform arrays. Involucres hemispheric, 3-6 mm diam. Phyllaries persistent, ca. 25 in 2-3 series, obscurely 2-3-nerved, lanceolate to linear, ± equal (herbaceous). Receptacles conic, epaleate. Florets 35-70+; corollas usually blue to purple or violet, rarely white, throats narrowly funnelform (lengths ca. 4 times diams.); styles: bases not enlarged, glabrous, branches filiform to linear-clavate. Cypselae prismatic (bases narrowed), 5-ribbed, glabrous or sparsely gland-dotted and/or hispidulous; pappi persistent, of ca. 30 barbellate bristles in 1 series. x = 10.