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 with opposite leaves, no stipules, and usually small perfect or polygamo-dioecious flowers, in corymbed panicled or capitate cymes. Calyx-tube adnate to the ovary, its limb inconspicuous or none in flower, often becoming prominent in fruit. Corolla gamopetalous, epigynous, somewhat irregular, its tube narrowed, and sometimes gibbous or spurred at the base, its limb spreading, mostly 5-lobed. Stamens 1-4, inserted on the corolla and alternate with its lobes, usually exserted. Ovary inferior, 1-3-celled, one of the cavities containing a single anatropous ovule, the others empty. Fruit indehiscent, dry, containing a single suspended seed. Endosperm little or none; embryo straight; cotyledons oblong.
About 9 genera and 300 species, of wide distribution, most abundant in the northern hemisphere. Fruit i-celled; persistent calyx-lobes becoming awn-like; tall herbs.
Fruit 3-celled; calyx-lobes minute or none; low herbs.