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, or in tropical regions rarely shrubs or trees, often with milky sap which contains a narcotic-acid poison, with alternate, exstipulate, simple, entire, toothed or pinnately parted leaves and solitary, spicate, racemose or paniculate flowers. Calyx-tube adnate to the ovary, its limb 5-lobed or 5-parted, the lobes equal or unequal. Corolla gamopetalous, irregular, often bilabiate, its tube open on one side nearly or quite to the base, its limb 5-lobed; stamens 5, inserted with the corolla; filaments sometimes cohering into a tube; anthers, united. Ovary 2-5-celled; style single; stigma fringed; ovules numerous, sessile, horizontal, anatropous. Fruit a 1-5-celled capsule, or a berry. Seeds numerous, with a smooth or furrowed testa. Endosperm fleshy.
About 20 genera and 600 species, of wide geographical distribution.