hazel, any plant of the genus Corylus of the family Betulaceae (birch family), shrubs or small trees with foliage similar to the related alders. They are often cultivated for ornament and for the edible nuts. Hazels are also called filberts, although the latter is more strictly a name for European kinds ( C. maxima, C. avellena, and their varieties, e.g., the cobnut) that are cultivated, chiefly in Europe, for the filbert of commerce. Nuts of the American hazel ( C. americana ) are often gathered but seldom sold. Winter hazel and witch hazel are not related to hazel. Hazel is classified in the division Magnoliophyta, class Magnoliopsida, order Fagales, family Betulaceae.