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Betulaceae, the birch family, includes six genera of nut-bearing and , including the , , , , , and numbering a total of 167 species. They are mostly natives of the temperate Northern Hemisphere, with a few species reaching the Southern Hemisphere in the in . Their typical flowers are and often appear before leaves.

In the past, the family was often divided into two families, Betulaceae ( Alnus, Betula) and Corylaceae (the rest). Recent treatments, including the Angiosperm Phylogeny Group, have described these two groups as subfamilies within an expanded Betulaceae: and . Diagnostically, Betulaceae is very similar to and other families.


Evolutionary history
The Betulaceae are believed to have originated at the end of the period (about 70 million years ago) in . This region at the time would have had a Mediterranean climate due to the proximity of the , which covered parts of present-day and into the early 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 . All six modern genera are believed to have diverged fully by the , with all genera in the family (with the exception of ) having a stretching back at least 20 million years from the present.

According to molecular phylogeny, the closest relatives of the Betulaceae are the , or the she-oaks.


Uses
The common hazel ( ) and the filbert ( ) are important plants, grown for their edible nuts.

The other genera include a number of popular , widely planted in parks and large gardens; several of the birches are particularly valued for their smooth, brightly coloured bark.

The is generally hard, tough and heavy, 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 , , , handles, chopping boards, and wooden pegs. In most of these uses, wood has now been replaced by or other man-made materials.


Subfamilies and Genera

Extant Species


Fossils


Phylogenetic systematics
Modern molecular phylogenetics suggest the following relationships:

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