9701318 Werth Graduate student Lilin Xiang, under the direction of Prof. Charles Werth at Texas Tech University, is studying the origin and diversification of the so-called male fern, Dryopteris filix-mas, over its wide northern-hemisphere distributional range. A polyploid plant, the male fern is thought to combine sets of chromosomes from two or possibly more parental diploid fern species that hybridized to produce doubled-chromosome offspring. Suspected diploid parents are Eurasian Dryopteris species, but American and Chinese taxa will also be studied. One goal is to distinguish between a single origin followed by dispersal, or multiple origins over the range of distribution, possibly from different parental species on the different continents. New evidence from molecular biology will help solve the problem, including electrophoretic analysis of protein variation (an indirect measure of genetic variability, sampling mostly nuclear genes) and direct DNA sequencing of a chloroplast gene. Population samples from North America, Europe, Turkey, and China are being gathered to provide extensive coverage of the morphological diversity known in this group of ferns. Polyploidy, or multiple sets of chromosomes (which sometimes restores fertility to otherwise sterile plant hybrids), is widespread in land plants, especially in ferns. As in the male fern, Dryopteris filix-mas, it is often associated with a widespread, almost weedy distribution, accompanied by minor morphological variation. Whether the polyploid arose once and dispersed widely to its present range, or arose through repeated hybridization events in various parts of the current distribution, is a question difficult to answer with only traditional taxonomic characters of morphology and anatomy. New molecular evidence from allozyme analyses and DNA sequencing, drawn from extensive population samples across the range and including several putative parent taxa, will help resolve the matter. In turn, the Dryopteris case will add to the small number of rigorous studies that analyze the historical biogeography of polyploid plant taxa.
