A widespread weed in tropical Amer. and s. U.S., has been collected as far n. as n. Ill. and se. Va. It will key to Calystegia, from which it obviously differs in its densely cymose-capitate clusters of blue fls ca 1 cm.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.