Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep 5, distinct, broad and herbaceous, persistent in fr; cor funnelform or shortly tubular-campanulate, resembling a small white morning-glory, the margin subentire or inconspicuously lobed, often 5-angled, in bud plicate and only inconspicuously twisted; stamens included or partly exsert; ovary bilocular, the style ± deeply bifid, the stigmas small and depressed-capitate; fr ovoid or globose, 2–4-valved, with (1)2(–4) seeds; cotyledons deeply bifid into linear segments; slender herbaceous perennial vines with soft, rather narrow lvs; fls in axillary, rather long-pedunculate cymes of 2–7 (or solitary at the end of the peduncle), the pedicels generally with a pair of small to rather large bracts somewhat below the fl. (Often included in Breweria or Bonamia) 6, Atlantic and c. U.S.