Plants 30-120(-200) cm. Stems lax, sprawling or scandent. Leaves: petioles (0.5-)1-3.5(-4) cm; blades triangular-deltate, (1-)2-5(-7) × (1-)1.5-3.5(-5) cm, bases usually truncate to cordate, sometimes obtuse, margins coarsely serrate to crenate-serrate, apices acute to acuminate. Involucres 4-5 mm. Phyllaries: outer lanceolate, inner lanceolate to narrowly oblong-lanceolate, glabrous or sparsely puberulent, apices usually acute to attenuate, sometimes rounded. Corollas usually pink-purple or whitish with pink to lilac lobes, rarely all white. Cypselae 1.8-2.8 mm, usually sparsely strigoso-hirtellous, sometimes glabrate. 2n = 20.
Stems weak, 3-12 dm, freely branching, each branch ending in a small infl; lvs opposite, petiolate, deltoid or somewhat cordate at base, tapering to the acuminate or acute tip, coarsely crenate-serrate, to 7 נ5.5 cm, trinerved; invol 3-5 mm, glabrous or nearly so, its bracts sharply acute to blunt, the main ones subequal, but some irregularly shorter outer ones also present; receptacle flat; fls (13-)18-24 per head, mostly pink-purple, seldom pale blue; achenes 5-8-nerved, glabrous or nearly so; 2n=20. Woods, ditch-banks, and swamps; se. Va. to Fla., w. to W.Va., s. Ind., s. Mo., Okla., Tex., and Mex. Sept., Oct.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
I have found this species in only three places in Indiana; in Harrison County, in the rather moist talus of a cliff along Blue River about half a mile north of White Cloud; and in Perry County, more or less frequent for a mile in moist places in the roadside ditch at the base of the high, wooded bluff along the Ohio River about 5 miles above Cannelton, and along the moist roadside of an abandoned road on the crest of the "German Ridge" about 6 miles east of Cannelton.