The Uncompahgre fritillary (Boloria acrocnema) is a species of butterfly in the Nymphalidae family. It is endemic to the United States. It is the last butterfly to be discovered in North America and was found by one Stanford University student, Larry Gall, and one University of Alberta student, Felix Sperling, working out of the Rocky Mountain Biological Laboratory. It was thought to be on the edge of extinction, but a number of additional populations have been found and the early monitoring programs that detected small numbers were found to be inadequate. The population is still considered to be endangered.