| Betulaceae | |
|---|---|
| Black Alder (Alnus glutinosa) | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| (unranked): | Rosids |
| Order: | Fagales |
| Family: | Betulaceae Gray |
| Genera | |
|
Alnus - Alder |
|
Betulaceae, or the Birch Family, includes six genera of deciduous nut-bearing trees and shrubs, including the 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); however, recent treatments, including the Angiosperm Phylogeny Group, have renamed these two groups as subfamilies within the Betulaceae- Betuloideae and Coryloideae.
The closest relatives of the Betulaceae are believed to be the Casuarinaceae, or the She-Oaks.
The Betulaceae are believed to have originated at the end of the Cretaceous period (c. 70 million years ago) in central China. This region at the time would have had a Mediterranean climate due to the proximity of the Tethys Sea, which covered parts of present-day Tibet and Xinjiang into the early Tertiary period. This point of origin is supported by the fact that all six genera and 52 species are native to this region, many of those being endemic. It is believed that all six modern genera had diverged fully by the Oligocene, with all genera in the family (with the exception of Ostryopsis) having a fossil record stretching back at least 20 million years from the present.
The Common Hazel (Corylus avellana) and the Filbert (Corylus maxima) are important orchard plants, grown for their edible nuts.
The other genera include a number of popular ornamental trees, widely planted in parks and large gardens; several of the birches are particularly valued for their smooth, brightly coloured bark.
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 In most of these uses wood has now been replaced by metal or other man-made materials.