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a family of dicotyledonous plants, often classified as a subfamily of the family Betulacea. They are monoecious shrubs or trees with alternate leaves and with unattractive unisexual flowers in catkin-like inflorescences (very reduced di-chasia). The family contains one genus, Corylus; more frequently the genera Carpinus, Ostrya, and Ostryopsis are included in the family. These four genera comprise more than 60 species, which grow primarily in the nontropical regions of the northern hemisphere. Two Mongolian-Chinese species of Ostryopsis and several species of the other genera of Corylaceae grow in the USSR.