Sep narrow, distinct, unequal in width; cor broadly campanulate to subrotate, lobed to below the middle; filaments on the cor-tube, abruptly dilated at base; ovary bilocular; ovules very numerous on the broad axile placentas; styles 2; capsule globose, subtended by the persistent cal, mostly breaking irregularly or 2-valved; seeds minute; ours perennial herbs with alternate, entire lvs, usually axillary spines, and small or medium- sized blue fls in axillary or terminal cymes. 11, mainly tropical.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
