Ha′zel, species of Corylus, a genus belonging to the birch family. The genus contains about seven species distributed throughout the northern hemisphere, three of which occur in the United States. The ordinary hazel, which often makes extensive thickets and produces the common wild hazelnut, is C. Americana. The beaked hazelnut (C. rostrata) is a fruit from a shrub extending from the northern part of North America south along the mountains. The third species occurs in California.