Annuals [perennials or subshrubs], 30-250 cm. Stems usually 1, erect or ascending, branched distally or ± throughout. Leaves mostly cauline; opposite; petiolate or sessile; blades usually 1-3-pinnately lobed [undivided], ultimate margins usually entire, faces usually glabrous, sometimes glabrate, hispid, puberulent, or scabridulous. Heads radiate, borne singly or in corymbiform arrays. Calyculi of [5-]8 basally connate, ± linear to subulate, herbaceous (striate) bractlets. Involucres hemispheric or subhemispheric [cylindric], 3-15 mm diam. Phyllaries persistent, [5-]8 in ± 2 series, distinct, lanceolate, lance-oblong, lance-ovate, or oblong, ± equal, membranous or herbaceous, margins ± scarious. Receptacles flat, paleate; paleae falling, linear, flat or slightly concave-convex, scarious (entire). Ray florets [0, 5] 8 (more in 'double' cultivars), neuter; corollas white to pink or purple, or yellow to red-orange. Disc florets 10-20[-80+], bisexual, fertile; corollas yellow [orange] (at least distally), tubes shorter than funnelform throats, lobes 5, ± deltate (staminal filaments hairy near anthers; style branches linear, flattened, thicker distally, hirtellous, appendages relatively slender). Cypselae (dark brown or black) relatively slender, quadrangular-cylindric or -fusiform [outer somewhat obcompressed], sometimes slightly arcuate, attenuate-beaked, not winged [winged], faces glabrous or hispid to scabridulous or ± setose, sometimes papillate, usually with 1 groove; pappi persistent [falling], of 2-4[-8] retrorsely [antrorsely] barbed awns, sometimes 0. x = 12.
Heads radiate, the rays neutral, white to pink, red, or yellow; invol bracts biseriate and dimorphic, the outer subherbaceous, the inner membranous or almost hyaline; receptacle flat, chaffy, its bracts plane; disk-fls perfect; style-branches slender, flattened, with short, hairy appendage; achenes quadrangular, not much compressed, linear, beaked; pappus of 2-8 retrorsely or rarely antrorsely barbed awns; herbs with opposite, simple to pinnately dissected lvs and subhemispheric heads. 20, warm New World.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.