The Betulaceaefamily includes deciduous trees and shrubs with simple and alternately located leaves. The flowers are unisexual and monocot. They are gathered in racemes lying on the main axis below the first flower where there are two axes ending in a flower in dichasial cymes. Most often these are grouped in tassels. The fruit is a nut with attached wings or located in a differently structured integument.
The family consists of6 genera and some 130 species. They are distributed primarily in the moderate climate regions of the northern hemisphere, except for several species found in the Andes Mountain.
It is believed that the family evolved at the end of Cretaceous some 70 million years ago in today’s Sichuan, Central China where the climate at that time resembled the Mediterranean climate because of the proximity of the Tethys Sea. This hypothesis is backed by the fact in this area are found 52 species and all 6 genera many of them being endemic. It is supposed that all six modern genera have fully diverged by Olygocene as they have all, except Ostryopsis, been found in fossils aged at least 20 million years.
The hazel speciesCorylus avellana Land Corylus maxima Millare grown commercially for the production of hazels. Some species, primarily the generaBirch(Betula), Hazel(Corylus) andHornbeam (Carpinus), are used as ornamental plants. The timber of the birches and especially of the hornbeam is hard, firm and heavy, and it was used in heavy weight elements of cart wheels as well as to make handles of tools etc.