Habit: monoecious shrubs or trees
Leaves: alternate, simple, stipulate
Flowers***: imperfect, regular; staminate inflorescence a catkin; pistillate inflorescences ***also a catkin of very reduced flowers
Sepals: 2-4 (6) and distinct in staminate flowers; 2-4, very reduced, connate and adnate to ovary or absent in pistillate flowers
Petals: absent
Stamens: 2-6, mostly distinct
Ovary: inferior (or superior) of 2 connate carpels with 1 locule above and 2 locules at base with 1 axile ovule per locule
Fruit: a nut or 2-winged samara
Diversity: 6 genera / 150 species
Distribution: of North Temperate regions or tropical mountains
Economics: Important riparian trees (Alder/ Birch); timber; nuts (hazelnuts or filberts); and cultivated ornamentals....