Evolution in plants often involves polyploidy, a doubling of the genome. Polyploidy is particularly common in ferns, where frequent episodes of interspecific hybridization and polyploidy have resulted in the formation of reticulate (or interrelated) species complexes in many genera. The evolutionary relationships within such groups of closely related species are often difficult to determine, particularly using traditional methods of analysis. Nowhere are the results of hybridization and polyploidy more evident than in Polystichum, a fern genus of nearly worldwide distribution consisting of 160 to 175 species. A prime example of the interrelated species groups typical of Polystichum and many other plant genera is found in the Polystichum complex from western North America, which contains five diploid and six polyploid species. In this investigation, molecular techniques (i.e., enzyme electrophoresis and analyses of DNA sequences) will be used to unravel the evolutionary relationships of these 11 species. This approach is potentially much more powerful than traditional analyses of plant structure and has not yet been applied to analyses of polyploid evolution in ferns; thus, this study may serve as a model for future investigations of hybridization and polyploidy. Not only will this project clarify the evolutionary relationships within the Polystichum complex from western North America, but it will also provide valuable insights into polyploidy, an important evolutionary process in both ferns and flowering plants.
