Townsend, J. F., and J. C. Ludwig. “Floristics of Difficult Creek Natural Area Preserve: A Piedmont Mafic Woodland Complex in Halifax County, Virginia, U.S.A.”. Journal of the Botanical Research Institute of Texas, Vol. 14, no. 2, Dec. 2020, pp. 481-19, doi:10.17348/jbrit.v14.i2.1024.