Genetic analyses of the lanceolatum clade in the genus Botrychium supports description of a new diploid species, Botrychium rubellum. It differs genetically, morphologically, and geographically from B. lanceolatum, from which it is segregated, and B. angustisegmentum. Botrychium rubellum is differentiated by the red coloration of the common stalk, upswept basal pinnae, basiscopic pinnules much longer than acroscopic pinnules, spores larger than the spores of the other two species, and in genetic identities reflecting the percent of shared alleles. Botrychium rubellum is currently known to occur in western North America from the southern Rocky Mountains to Alaska, the Yukon Territory, and disjunctively to Greenland.