Little, Elbert L. National Audubon Society Field Guide to North American Trees:
Eastern Region. Chanticleer Press, New York. 1980

Online Botanical Glossary

Petrides, George A. A Field Guide to Trees and Shrubs: Northeastern and north-central
United States and southeastern and south-central Canada (The Peterson Field Guide Series). Houghton and Mifflin. 1973

Symonds, George W. D. The Shrub Identification Book. HarperCollins Publishers Inc.,
Manhattan. 1963

University of Illinois Website.