This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs, some tropical species shrubs or trees, the stems twining, ascending, trailing or erect, with alternate exstipulate entire dentate lobed or dissected leaves, and regular perfect axillary cymose or solitary flowers. Calyx inferior, 5-parted or 5-divided, usually persistent, the segments or sepals imbricated. Coralla gamo-petalous, funnelform, salverform, campanulate, tubular or rarely subrotate, the limb 5-angled, 5-lobed or entire. Stamens 5, inserted low down on the tube of the corolla and alternate with its lobes, all anther-bearing, the filaments filiform, or dilated at the base, equal or unequal; anthers 2-celled, the sacs longitudinally dehiscent. Disk annular or none. Ovary superior, sessile, 2-3-celled, with 2 ovules in each cavity, or falsely 4-6-celled with a single ovule in each cavity, entire or 2-4-divided; styles 1-3, terminal, or arising from between the ovary-divisions; ovules anatropous. Fruit a 2-4-valved capsule or of 2-4 distinct carpels, in our species. Seeds erect, the testa villous, pubescent or glabrous; embryo plaited or crumpled; cotyledons foliaceous; endosperm fleshy or cartilaginous, usually scanty.
About 45 genera and probably 1000 species, of wide geographic distribution, most abundant in the tropics.
Style 2-cleft or 2-divided. Style 2-cleft or 2-parted.
Style 2-divided to the ovary, each division 2-cleft.
Style entire up to the stigma.
Stigma or stigmas capitate or globose.
Corolla salverform; stamens and style exserted.
Corolla funnelform or campanulate; stamens and style included.
Stigmas 2, filiform to oblong.