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..
Herbs, some exotic genera low shrubs, with alternate or opposite simple mostly entire thin leaves. Flowers small, green or white, perfect, monoecious, polygamous, or dioecious, bracteolate, variously clustered, usually in terminal spikes or axillary heads. Petals none. Calyx herbaceous or membranous, 2-5-parted, or 5-cleft, the segments distinct or somewhat united, equal, or the inner ones smaller. Stamens 1-5, mostly opposite the calyx-segments, hypogynous; filaments distinct, united at the base, or into a tube; anthers 1-celled or 2-celled. Ovary ovoid or subglobose, 1-celled; ovule solitary in the following genera, amphitropous (several in some tropical genera); style short, elongated or none; stigmas 1-3. Fruit a utricle, circumscissile, bursting irregularly or indehiscent, 1-seeded in our genera. Seed mostly smooth; embryo annular; endosperm mealy, usually copious.
About 40 genera and 475 species, widely distributed, most abundant in warm regions.
Anthers 2-celled; leaves alternate.
Calyx 2-5-parted or of 2-5 sepals.
Calyx of the pistillate flowers wanting.
Anthers 1-celled; leaves opposite.
Flowers in small axillary clusters.
Flowers variously spicate or paniculate.
Calyx 5-cleft; filaments united into a tube.
Calyx 5-parted; filaments united at the base.