With its thick, leathery leaves, reticulate venation, and large sori, Polypodium scouleri, located in a narrow band along the Pacific coast of North America, is the most distinctive member of the cosmopolitan P. vulgare species complex. Although early studies based on morphology and chromosomes yielded hypotheses about the relationships among some elements of this complex, phylogenetic alliances to P. scouleri were not proposed. Combining data from rbcL and trnL DNA sequences with isozymic analyses suggested that P. scouleri originated relatively recently and is closely allied to and sympatric with P. californicum and P. glycyrrhiza. Consistent with a hypothesis of recent origin, we detected no infraspecific isozymic variation across the range of P. scouleri. Although allopolyploidy is a common feature of the P. vulgare complex, P. scouleri stands out because it has not been implicated in the origin of any secondary (allotetraploid) species. However, as early as 1951, Manton reported a triploid individual that was morphologically similar to P. scouleri, but whose other parent could not be verified. Since that time, others have suggested that P. scouleri might be crossing with sympatric congeners, but no solid evidence has been obtained. The present study confirmed that P. scouleri hybridized with neighboring P. calirhiza, and showed that individuals with intermediate morphological features contained isozyme marker alleles from both parental lineages.