Botrychium furculatum S. J. Popovich & Farrar is a new species widespread in the central and southern Rocky Mountains from Alberta and Montana south to New Mexico, with additional populations in the Cypress Hills of Saskatchewan and the Black Hills of Wyoming and South Dakota. Based on allozyme banding patterns, it is inferred to be an allotetraploid with B. pallidum W. H. Wagner as one parent and another, as yet undescribed, diploid species (B. “farrarii”) as the other parent. Genetically, B. furculatum is distinguished from B. pallidum by exhibiting fixed heterozygous loci in which expressed alleles of one of the genomic contributions matches those of B. pallidum, whereas many alleles of the other genomic contribution have not been detected in B. pallidum, but are displayed by B. “farrarii.” Morphologically, a suite of leaf characters differentiates B. furculatum from B. pallidum, particularly a more pronounced bowed or wishbone-like junction of sporophore and trophophore. Gradations in morphology and color between the two species have led to erroneous reports of B. pallidum in the Rocky Mountains. A key to differentiate B. furculatum from similar species is presented.