Characteristics and Interesting Facts The hazel (Corylus) is a genus of deciduous trees and large shrubs native to the temperate Northern Hemisphere with 14–18 species . The genus is usually placed in the birch family Betulaceae, though some botanists split the hazels (with the hornbeams and allied genera) into a separate family Corylaceae. Hazel requires a winter chilling period of 800 – 1200 hrs below 7 C (45…