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 even trees), with alternate exstipulate leaves, usually milky juice, and racemose spicate paniculate or solitary perfect flowers. Calyx-tube adnate to the ovary, its limb mostly 5-lobed or 5-parted, the lobes equal or slightly unequal, valvate or imbricate in the bud, commonly persistent. Corolla gamopetalous, regular, inserted at the line where the calyx becomes free from the ovary, its tube entire, or deeply cleft on one side, its limb 5-lobed. Stamens 5, alternate with the corolla-lobes, inserted with the corolla; filaments separate; anthers 2-celled, introrse, separate or connate. Ovary 2-5-celled (rarely 6-10-celled, with the placentae projecting from the axis, or 1-celled with two parietal placentae; style simple; stigma mostly 2-5-lobed; ovules anatro-pous. Fruit a capsule. Seeds very numerous and small; embryo minute, straight; endosperm fleshy.
About 40 genera and over 1000 species, of wide geographic distribution.
Capsule opening by lateral pores or valves.
Corolla campanulate, rarely rotate; flowers all complete.
Corolla rotate; earlier flowers cleistogamous.
Capsule opening by terminal pores or valves.