Penstemon debilis O’Kane and Anderson (Scrophulariaceae) is known from only five populations in Garfield Co., Colorado. It is an oil-shale talus endemic restricted to the Green River Oil Shale formation. Populations are found on steep, south-facing slopes from 8500-9000 ft. Penstemon debilis is a candidate for listing under the Endangered Species Act, and it is considered to be at severe risk of extinction. Studies initiated on the breeding systems, pollination biology, seed predation, seed germination, soil characterization and genetic diversity will contribute to a management plan for the conservation of this rare species. We sampled leaf material from 114 individuals from the five known populations of P. debilis for ISSR analysis. ISSR banding patterns were used to assess whether outbreeding depression contibuted to lower seed set in experimental crosses between populations and to assess the genetic diversity within and between populations of P. debilis.

Key words: conservation biology, genetic diversity, ISSR, Penstemon, Scrophulariaceae