HAUFLER, C. H.1*, T. HILDEBRAND1, P. HAMMOND2, J. P. THERRIEN1, AND C. WALTERS1. 1 Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS, 2University of California Botanical Garden, San Francisco CA . - New insights concerning the origin of Polypodium scouleri and its ongoing hybridization with sympatric congeners.
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