Peter Raven, in 1963, included two fern taxa of the genus in his list of plant species exhibiting American amphitropical bipolar disjunctions. He attributed the southern hemisphere occurrences to post-Pleistocene long-distance dispersal from counterparts in the northern hemisphere, probably assisted by annual bird migrations between the disjunct areas. Using genetic evidence gathered through worldwide analyses of phylogenetic relationship in, we now review and reconsider Raven's conclusions. Genetic similarities indicate that South American is an allotetraploid taxon closely related to, a North American endemic, and that in New Zealand possesses a genotype identical to that of a taxon in North America derived through introgressive hybridization between and an endemic North American species, Both North American counterparts exhibit Raven's characteristics of bipolar disjuncts in their occurrence in mountain and coastal meadows, copious production of small propagules (spores in), occurrence in habitats frequented by transpolar bird migrants, and ability to found new colonies through inbreeding. We discuss these characteristics in and relative to other ferns and suggest further studies on and related taxa to address questions of time, number, and mode of bipolar dispersals.