Dryopteris dilatata  in the British Isles

Erin Sigel, who was a masters' student in my lab and is now working towards her Ph.D. with Kathleen Pryer at Duke, contributed substantial insights into the pattern of polyphyletic origins in the polyploid species complex including our northeastern mountainwoodfern Dryopteris campyloptera and its European counterpart Dryopteris dilatata.  
                The following summary is taken from the abstract to Erin's thesis.  She addressed the evolutionary and biogeographic histories of two allotetraploid species of the homosporous fern genus Dryopteris section Lophodium (Dryopteridaceae), North American Dryopteris campyloptera and European Dryopteris dilatata, using maternally and biparentally inherited molecular markers. Previous artificial hybrid-synthesis experiments identified their diploid progenitors as the circumboreal Dryopteris expansa and a member of the Dryopteris intermedia aggregate, while morphological observations and cpDNA phylogenies of the genus provided evidence for separate origins of the allotetraploid taxa. In this study trnL-F and rps4-trnS cpDNA sequences, gapCp nuclear DNA sequences, and amplified fragment length polymorphisms (AFLPs), considered in the light of isozyme electrophoresis data, identified a minimum number of origins of the allotetraploids and inferred the geographic provenance of their genomes. The gapCp phylogeny and AFLP neighbor-joining network support a hypothesis of separate origins, and implicate North American D. intermedia as the maternal progenitor of D. campyloptera. Conversely, autapomorphies of D. dilatata suggest an unsampled, perhaps extinct, European maternal progenitor genetically similar to D. intermedia. Lack of resolution among progenitor populations in the cpDNA phylogeny and AFLP principal components analysis, viewed in the context of current distributions, suggests a recent biogeographic history for the group shaped by Pleistocene glaciations