The genus Hazelnut, Corylus, is in the Birch Family, Betulaceae.
The state distribution maps in the species info boxes below are from the USDA NRCS PLANTS Database at plants.usda.gov. In instances where state specific maps are unavailable, the US distribution map will be used in its place. Also, the PLANTS Database website states "Our county data are based primarily on the literature, herbarium specimens, and confirmed observations. However, not all populations have been documented, so some gaps in the distribution shown above may not be real. Remember that only native and naturalized populations are mapped!"
Search all North American native Hazelnut species here.