Much like Convolvulus in aspect, but the bracts usually large, inserted just beneath the cal, and ±concealing it; pollen spheroidal, pantoporate with 20-40 apertures; ovary ±unilocular, the partition incomplete; stigmas oblong, ±cylindric, blunt; fls usually solitary; our spp. rhizomatous perennials. 30, widespread.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.