This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Handsome shrubs or herbs of trailing, twining or climbing habit, or more rarely erect. Leaves usually opposite, compound or simple, exstipulate. Calyx inferior, entire or lobed or spathaceous. Corolla regular or irregular. Stamens 5, of which 4 or only 2 are fertile. Fruit a dry frequently woody capsule, 2-celled with a central placentation, or 1-celled with parietal placentation. Seeds compressed, winged, destitute of albumen. There are about fifty genera, comprising 450 species, for the greater part inhabitants of tropical regions.