Aggressive perennial from deep-seated spreading roots; trailing or climbing to 1 m, often forming tangled mats; lvs variable, triangular to oblong in outline, 1-5 cm, the basal lobes spreading or descending; peduncles axillary, exceeding the subtending lvs, 1-2-fld; bracts subulate to ovate, 1-10 mm, inserted 5-20 mm below the fl; sep elliptic to subrotund, 3-5 mm; cor white or pink, 15-25 mm; 2n=48, 50. Native of Europe, now a common weed in fields, roadsides, and waste places in the U.S. and s. Can. May-Sept. (Strophocaulos a.; C. ambigens, a hairy form)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.