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, shrubs, or trees, with simple, opposite or sometimes verticillate. mostly stipulate leaves, and perfect, often dimorphous or trimorphous, regular and nearly symmetrical flowers. Calyx-tube adnate to the ovary, its limb various Corolla gamopetalous, funnelform, club-shaped, campanulate, or rotate, 4-5-lobed, often pubescent within. Stamens as many as the lobes of the corolla and alternate with them, inserted on its tube or throat; anthers mostly linear-oblong. Ovary 1-10-celled; style short or elongated, simple or lobed; ovules 1-00 in each cavity. Fruit a capsule, berry, or drupe. Seeds various; seed-coat membranous or crustaceous; endosperm fleshy or horny (wanting in some exotic genera); cotyledons ovate, cordate, or foliaceous.
About 340 genera and about 6000 species, of very wide geographic distribution, most abundant in tropical regions. Known as Madderworts.
* Leaves opposite, stipulate (sometimes verticillate in No. 3). Ovules numerous in each cavity of the ovary; herbs.
Top of the capsule free from the calyx; seeds few, peltate.
Capsule wholly adnate to the calyx; seeds minute, angular.
Ovules 1 in each cavity of the ovary.
Shrubs or small trees; flowers in dense globular heads.
Low evergreen herbs; flowers 2 together, their ovaries united.
Herbs; flowers axillary, nearly sessile, distinct.
Capsule separating into 2 carpels, one dehiscent, the other indehiscent.
Capsule separating into 2 (or 3) indehiscent carpels.
** Leaves appearing verticillate; herbs (some of the leaves rarely opposite in No. 7); ovule 1 in each cavity of the ovary. Corolla rotate; calyx teeth minute or none.
Flowers in involucrate heads.
Flowers in panicles.