Botrychium ascendens is reported from Fogo Island in Newfoundland as an addition to the flora of the province. Fogo Island plants are identical to plants in western North America, including those from the type locality, in comparisons of leaf morphology, spore size, and allozyme expression. Comparisons are made with related and confusing taxa, B. campestre, B. crenulatum, B. lineare, and the American genotype of B. lunaria. Newfoundland plants display a high level of fixed heterozygosity and large spore size, indicating they are allotetraploid, and supporting suggestions that B. ascendens is derived from ancient hybridization between B. crenulatum and the B. lineare/campestre complex. The current distribution of Botrychium ascendens and its putative parents suggest it probably originated in western North America and migrated across northern Canada to Newfoundland.