THE BIRCH / HAZEL FAMILY (Betulaceae)

This family includes six genera of deciduous nut-bearing trees and shrubs, including birches, alders, hazels, hornbeams and hop-hornbeams, numbering about 130 species. They are mostly natives of the temperate Northern Hemisphere, with a few species reaching the Southern Hemisphere in the Andes in South America. In the past, the family was often divided into two families, Betulaceae (Alnus, Betula) and Corylaceae (the rest). Recent treatments, including that of the Angiosperm Phylogeny Group, have described these two groups as subfamilies within an expanded Betulaceae: Betuloideae and Coryloideae. Betulaceae are believed to have originated at the end of the Cretaceous period (about 70 million years ago) in central China. All six modern genera have a fossil record stretching back at least 20 million years from the present. Some are grown for their edible nuts (hazel), others as ornamental trees, (some birches in particular for their beautiful bark), others for their timber. The wood is generally hard, tough and heavy, hornbeams particularly so; several species were of significant importance in the past where very hard wood capable of withstanding heavy wear was required, such as for cartwheels, water wheels, cog wheels, tool handles, chopping boards and wooden pegs. In most of these uses, wood has now been replaced by metal or other man-made materials.

Leaves are generally of simple shape (not sub-divided) with toothed, sometimes doubly toothed margins, rarely smooth. Flowers are wind pollinated and single-sexed with separate male and female flowers occurring on the same plant. The male flowers occur in long hanging inflorescences known as catkins, female flowers are tiny and often difficult to see, with small bract-like leaf structures protecting the ovaries. They are arranged singly or in small clusters directly on the stem or in hanging catkins. Fruits are in the form of nuts or winged nuts with one seed each.

(source: Wikipedia)