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 with a watery juice. Leaves deciduous, alternate, simple, usually more or less hispid, and often oblique at the base. Stipules caducous. Flowers hermaphrodite or polygamous, arranged in clusters or fascicles. Perianth inferior, persistent, 4- to 9-lobed. Stamens 4 to 9; filaments adnate to the perianth. Fruit 1- or 3-celled, indehiscent, drupaceous or membranous, and furnished with a circular wing. Seeds solitary, pendulous. This order includes about six genera and fifty species. Natives of the northern temperate zone.