Polyploidy, the multiplication of chromosome sets above the diploid state, is arguably as prevalent in plants as any other eukaryotic group. Over the past century, polyploidy has been linked with particular taxonomic groups (flowering plants, ferns), northern latitudes and extreme environments, and life histories such as perenniality, asexuality and self-fertilization. Here we review the current state of evidence for these patterns and their interpretations. Our understanding of the incidence of polyploidy in plants is still in flux due to a progression of advances in cytogenetics, flow cytometry, phylogenetics and genomics. We find polyploidy to be highly heterogeneous among plant groups and estimates of intraspecific variation and hybrid forms are increasing with high throughput analyses. Surprisingly, many accepted trends between polyploidy and geography, mating system, and comparative rates of species diversification have become less strong or conflicting with the development of new procedures, in particular with phylogenetic approaches. Our review suggests that while some patterns remain strong, many are not universal, suggesting there may be no unified explanation for the success of polyploids in plants.