PHYLOGENY OF THE POLYPODIUM-VULGARE COMPLEX - INSIGHTS FROM CHLOROPLAST DNA RESTRICTION SITE DATA

Analysis of chloroplast DNA restriction site data was applied to members of the taxonomically troublesome Polypodium vulgare complex. In this group, chromosomal and isozyme analyses had clarified reticulate patterns of speciation, but had failed to generate robust hypotheses of diploid phylogeny. DNA's of five diploid and Eve tetraploid species, plus two outgroup species, were digested with 11 endonucleases and hybridized to fern chloroplast DNA probes, yielding 60 informative site changes. Restriction site mapping revealed that the general size and structure of the chloroplast genome in Polypodium species corresponds closely to those of other ferns. The mean sequence divergence among diploid Polypodium species (0.017) was high compared to results for congeneric species of seed plants. Using P. plesiosorum and Pleopeltis angusta as outgroups, the monophyly of the P. vulgare complex was supported by at least 17 synapomorphies. Within the complex, two distinct diploid species groups (P. glycyrrhiza + P. californicum and P. amorphum + P. appalachianum + P. sibiricum) were separated by a minimum of 28 restriction site mutations. Molecular data also revealed multiple and, in three cases, reciprocal origins of the tetraploids.