P.D.Cantino (Shinners) 1982 - Cantino PD (1982) A MONOGRAPH OF THE GENUS PHYSOSTEGIA (LABIATAE). Contributions From The Gray Herbarium of Harvard University 211: 1-105. Retrieved from http://www.jstor.org/stable/41764739
There is no corrections for Physostegia virginiana subsp. praemorsa yet.