201908 Willow Oak (Quercus phellos) Illustration USDA-NRCS PLANTS Database Britton, N.L., and A. Brown. 1913
%20Illustration%20USDA-NRCS%20PLANTS%20Database%20%20Britton%2C%20N.L.%2C%20and%20A.%20Brown.%201913.jpg "201908 Willow Oak (Quercus phellos) Illustration USDA-NRCS PLANTS Database Britton, N.L., and A. Brown. 1913.jpg")
Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada.
USDA, NRCS. 2024. The PLANTS Database (http://plants.usda.gov). National Plant Data Team, Greensboro, NC 27401-4901 USA.