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.
This is a somewhat anomalous group of shrubs and trees. Leaves usually stipulate and alternate, simple, entire, toothed or lobed. Flowers often small and unisexual, usually in dense heads. Fruit a woody capsule, 2-celled, 2- or many-seeded. About fifteen genera, and as many more species, are referred here.