This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", 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..
Annual or perennial herbs with opposite entire leaves, estipulate or stipulate, and mostly small perfect flowers, solitary or in cymes or umbels. Calyx of 4 or 5 sepals, imbricated, at least in the bud, separate to the base, or nearly so. Petals as many as the sepals, not clawed, rarely wanting. Stamens twice as many as the sepals, or fewer, inserted at the base of the sessile ovary, or on a small disk; filaments distinct, or cohering below; anthers introrse, longitudinally dehiscent. Ovary usually I-celled; styles 2-5, distinct; ovules several or numerous, amphi-tropous or campylotropous, borne on a central column. Fruit a capsule, dehiscent by valves or by apical teeth. Embryo mostly curved and with incumbent cotyledons.
About 32 genera and 500 species, of wide distribution, most abundant in temperate regions. Styles separate to the base.
Plants not fleshy; disk of the flower inconspicuous or none.
Petals deeply 2-cleft or 2-parted (rarely none).
Capsule ovoid or oblong, dehiscent by valves.
Capsule cylindric, commonly curved, dehiscent by teeth.
Petals entire or emarginate (rarely none).
Capsule ovoid or oblong.
Styles as many as the sepals, alternate with them.
Styles fewer than the sepals.
Seeds not appendaged by a strophiole.
Plants fleshy, maritime; disk conspicuous, 8-10-lobed.
Stipules present, scarious.
Styles and capsule-valves 5.
Styles and capsule-valves 3.
Styles united below; southwestern herb with subulate leaves.