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.
Trees, shrubs, or rarely herbs, usually with a milky sap. Leaves simple, opposite, or more rarely alternate or whorled. Stipules none, or sometimes replaced by bristles or glands between the petioles. Flowers regular, solitary or corymbose, axillary or terminal. Calyx free, 4- or 5-lobed. Corolla hypogynous, salver-shaped or campanulate, throat naked or hairy, lobes twisted in bud. Stamens 4 or 5, inserted on the tube of the corolla; anthers connate and adhering to the stigma; stigma usually constricted in the middle. Fruits usually composed of two many-seeded follicles; capsules rarely drupoid or baccate. Seeds often winged or plumose. With the exception of the genera coming within our province, the members of this order are tropical or sub-tropical, and most numerous in Asia. There are about 100 genera and 600 species known.