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 deciduous trees, often with a resinous juice. Leaves alternate, unequally pinnate, exstipulate. Flowers small, dioecious, inconspicuous, often appearing before the leaves; males in catkins, females solitary or clustered. Calyx irregularly lobed. Petals very small or wanting. Fruit a drupe, inferior, 2- or 4-celled at the base, and 1-celled at the apex, 1-seeded. Seed destitute of albumen, wrinkled and lobed, or divided by the partial dissepiments. There are four genera, including less than thirty species, natives of the temperate or warm parts of the northern hemisphere.