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.
Highly ornamental deciduous trees with large elegantly lobed leaves on long petioles, and conspicuous sheathing stipules. Flowers destitute of perianth, monoecious, in separate naked spherical bracteolate solitary or clustered catkins, on long pendent peduncles. Male flowers with 1 stamen. The 1-celled 1- or 2-seeded nuts or achenes, are arranged in dense heads. The order is restricted to a solitary genus whose few species occur in North Africa, Western Asia, and North America.