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 perhaps the most distinctive member of the cosmopolitan P. vulgare species complex. Although early studies based on morphology and chromosomes were able to develop hypotheses about the relationships among some elements of this complex, no close alliances to P. scouleri could be proposed. Combining data from rbcL and trnL DNA sequences with isozymic analyses suggests that P. scouleri is a recently evolved species that is closely allied to and sympatric with P. californicum and P. glycyrrhiza. Alternatively, because isozyme data indicate that P. scouleri is quite distinct from its sympatric neighbors, hybridization between these lineages may have led to chloroplast capture prior to range expansion of P. scouleri. Adding further intrigue is that P. scouleri contrasts strikingly with its congeners in having never been implicated in the origin of allotetraploid derivatives. As early as 1951, Manton suggested that P. scouleri could be forming hybrids with neighboring polypods, but she was sufficiently unsure of the morphology to request, "a purer sample of P. scouleri," before stating positively that hybrids had been discovered. Since that time, others have suggested that P. scouleri might be involved in hybridization, but no solid evidence has been obtained. Using isozyme techniques, we have detected little or no infraspecific variation across the range of the species. We have been able to confirm that P. scouleri is hybridizing with neighboring P. californicum and/or P. calirhiza. Individuals that appear to be intermediate in morphology contain isozyme marker alleles from two putative lineages. We are currently characterizing these hybrids further and studying the dynamics of this interesting population and species.

Key words: hybridization, isozymes, Polypodium scouleri, Polypodium vulgare complex