Barner, J. 2008. Propagation protocol for production of propagules (seeds, cuttings, poles, etc.) Penstemon acuminatus Douglas ex Lindl. seeds. Native Plant Network. U.S. Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources. http://npn.rngr.net/propagation/protocols [Accessed 2020 June 5].