Genera
Alnus*
Betula*
Carpinus
Corylus*
Ostrya
Ostryopsis
*Pictures on right

Primary sources
Heywood
1978
Slides by R. J. Shaw and Melissa Lloyd

Size: The Betulaceae is a small family, having only 6 genera and 170 species.  Shaw (1989) lists 8 species as occuring in northern Utah, but 4 of them are introduced.

Distribution: The Betulaceae is primarily a north temperate family, but some species extend into South America via the mountains.

Importance:  To any Canadian or Native American, the family must be treasured for Betula papyrifera, the source of birch bark for canoes and brilliant white trunks that surround the northern lakes.  Corylus is the source of hazelnuts, filberts, and cobnuts.  The first two are delicious.  I know nothing about the third.  Ostrya has extremely hard wood and is used for making mallets.  Betula and Alnus are also used for furniture and woodwork. 

Morphology: All members of the Betulaceae are wind-pollinated, monoecious trees or shrubs. The leaves are simple, alternate, serrulate to serrate, deciduous, and have stipules. The individual flowers are minute, but they are generally clustered in conspicuous inflorescences. An exception to this statement is provided by the pistillate flowers of Corylus, (hazelnut or filbert). First the general case. Both the staminate and the pistillate flowers may be aggregated in cymose groups of three. The staminate flowers have 2-12 stamens and a variable number of scales. These flowers are aggregated into long, flexible, dangling catkins. The pistillate flowers consist of a single, bicarpellate pistil. The groups of three flowers are borne on a stiff axis which is sometimes upright. In Alnus, the pistillate inflorescence is woody and is sometimes referred to (incorrectly) as a cone. In Betula (birch), the pistillate inflorescence breaks up at maturity. In Corylus, both the staminate and the pistillate flowers are single rather than aggregated in groups of three. This makes the catkin of Corylus a spike; the pistillate flowers are solitary. Look for them at the start of the quarter; their styles look like two red threads coming out of a bud. Those in the picture are a trifle old. 

Alnus incana
Pistillate inflorescence from this year and last year; simple, doubly serrate leaf.

Betula glandulosa
Simple, serrate leaf

Betula pendula

Betula pendula
Staminate catkin above;
pistillate catkin below

Betula occidentalis
Doubly serrate leaves

Corylus maxima
Pistillate inflorescence