Chloroplast DNA evolution and systematics of Phanerophlebia (Dryopteridaceae) and related fern genera.

Restriction site variation in chloroplast DNA was examined in the neotropical fern genus Phanerophlebia and in selected species of the related Asiatic genus Cyrtomium and the cosmopolitan progenitor of these two, Polystichum. A total of 103 restriction site mutations was identified; these were used to construct phylogenetic networks and trees based on Wagner and Dollo parsimony and Fitch-Margoliash distance algorithms. The analyses provided evidence that Phanerophlebia did not arise from Cyrtomium. Both genera are convergent descendants from different progenitor groups in Polystichum, and Asiatic Cyrtomium is more closely related to temperate New World Polystichum than it is to neotropical Phanerophlebia. Reticulate venation, previously considered an important taxonomic character for infrageneric classification in Phanerophlebia, most likely evolved independently twice within the genus. Diploid maternal progenitors are suggested for two of four tetraploid species analyzed, and species-level distinctions for two closely related taxa of Phanerophlebia are questioned.