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..
Perennial herbs, shrubs, vines, or some tropical genera trees, mostly with an acrid milky juice, with simple opposite alternate or verticillate exstipulate leaves, and perfect regular 5-parted cymose solitary or paniculate flowers. Calyx inferior, persistent, the lobes imbricated in the bud. Corolla gamopetalous, its lobes convolute in the bud and often twisted. Stamens as many as the lobes of the corolla, alternate with them, inserted on the tube or throat; anthers linear-oblong, or sagittate, 2-celled; pollen-grains simple, often glutinous. Ovary superior, or its base adherent to the calyx, of 2 distinct carpels, or i-celled, with 2 parietal placentae, or 2-celled; ovules few or numerous, anatropous or amphitropous; style simple, or 2-divided; stigma simple. Fruit usually of 2 follicles or drupes. Seeds often appendaged by a coma; endosperm fleshy, not copious; embryo straight; cotyledons flat or concave; radicle terete, usually shorter than the cotyledons.
About 130 genera and 1100 species, very widely distributed, mostly in tropical regions. Leaves alternate; erect herbs.
Leaves opposite; vines or herbs. Flowers large, axillary, solitary.
Flowers small, cymose.
Erect or diffuse herbs; corolla campanulate.