Prefers sandy soil in dry situations but adapts itself to moist conditions. Rather frequent in the southern half of the state in open woodland, pastures, and fallow fields and along roadsides. Our Steuben County specimen was collected in 1928 by Anna May Weatherwax on the border of a cornfield along Little Crooked Lake northwest of Angola. No doubt this specimen was adventive. The species has a weedy nature. I had it under cultivation several years ago and it reproduced so abundantly that I feared it might become a weed so I exterminated it.
Erect, weedy annual, 1.5-6 dm, sparingly branched, very viscid-hairy throughout; lvs long-petioled, lanceolate to ovate, 2-5 cm; fls solitary or paired in the upper axils, short-pedicellate; hypanthium nearly 1 cm; pet red-purple, clawed, the upper 2 the largest, ca 8 mm; 2n=12. Dry soil; N.H. to n. Ill. and Kans., s. to Ga. and La., commoner southward. July-Sept. (C. petiolata, a preoccupied name)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.