Ogle, D.G.; Peterson, J.S.; St. John, L. 2014. Plant guide: Rocky Mountain penstemon (Penstemon strictus). Aberdeen, ID: U.S. Department of Agriculture, Natural Resources Conservation Service, Plant Materials Center. 4 p.
Ogle, D.G.; Peterson, J.S.; St. John, L. 2014. Plant guide: Rocky Mountain penstemon (Penstemon strictus). Aberdeen, ID: U.S. Department of Agriculture, Natural Resources Conservation Service, Plant Materials Center. 4 p.