Wetherwax, Margriet; Holmgren, Noel H. "Penstemon azureus". Jepson eFlora. University of California, Berkeley. Archived from the original on 9 July 2024. Retrieved 27 October 2024.
Penstemon azureus, USDA Natural Resources Conservation Service PLANTS Profile, 29 October 2024
web.archive.org
Wetherwax, Margriet; Holmgren, Noel H. "Penstemon azureus". Jepson eFlora. University of California, Berkeley. Archived from the original on 9 July 2024. Retrieved 27 October 2024.