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.
Deciduous trees or shrubs with alternate or opposite simple or compound leaves and usually polygamous flowers. Stamens unequal, or double the number of the petals, or if equal alternate with them, inserted within, upon or around the disk. Ovary 1- to 3- (rarely 4-) celled, with 1 style. Fruit variable. This order includes an assemblage of genera of somewhat heterogeneous appearance and structure to the number of 73, containing between 600 and 700 species.