In plants, reproductive isolation is commonly achieved through the doubling of nuclear DNA content (genome-wide duplication). Such polyploidization events are hypothesized to occur when incomplete meiosis forms diploid (2n) gametes which unite to form polyploid (4n) progeny. These resulting polyploid progeny and diploid progenitors, are reproductively isolated and may be considered biological species. This model frames polyploid speciation as a frequency dependent process where production of 2n gametes is expected to determine the prevalence of polyploid species. Despite the near universal acceptance of this model in biology textbooks, the predicted relationship between 2n gamete production and polyploid diversification remains untested. Ferns, having a high rate of polyploidy, are an ideal system in which to evaluate this model. We propose to estimate the predicted correlation between diploid gamete production and polyploid diversity at both genus and population levels. Flow cytometry will be used to estimate the 2n gamete production, while phylogenetic and cytological databases will be used to estimate polyploid occurrence at the genus level. After sampling, phylogenetic contrast methods will be used to quantify correlated evolution of these parameters across the fern phylogeny. If unreduced gamete frequency determines polyploid speciation, a significant positive correlation will be observed in the sampled species. These tests will determine whether the rate of fern polyploid speciation is driven by ploidal mutation pressure, or if differential survival and reproduction between diploids and their polyploids is a more important determinant of polyploid occurrence and diversification.