Leaves alternate, simple, with stipules
Flowers unisexual, highly reduced, in catkins, wind-pollinated
Fruit a 1-seeded samara or nut
6 genera, 120 species
Economic importance - timber from birches, hazel nuts
Diagnostic characters - deciduous trees or shrubs, leaves serrate, staminate flowers in catkins, pistillate flowers in coneline catkins
Unusual charcteristics - Alnus (alders) fix nitrogen in nodules on roots
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