| Dryopteris (Dryopteridaceae), the wood or shield ferns, is an ideal genus with which to investigate a number of phenomena that have historically been understudied in ferns. Ferns are genetically and ecologically unique among land plants, but have received relatively little attention from plant biologists compared to their sister group, the seed plants. The current study presents the most comprehensive phylogenetic analyses of Dryopteris to date, based on sequences from the plastid and nuclear genomes. These phylogenies are used to examine phylogenetic and biogeographic relationships, hybridization, and polyploidy, and provide a framework for field and common-garden investigations of morphological and physiological adaptation. Based on analyses of seven plastid loci, Dryopteris is shown to be approximately 42 million years old, and the existing classification system for the genus does not reflect phylogenetic relationships. The thirty species in the New World are not monophyletic, and taxa from North, Central, and South America are most closely related to species from Eurasia and/or Africa. Among the Latin American species, phylogenetic analysis of the nuclear marker pgiC reveals that extensive hybridization has occurred involving Asian ancestors and long distance dispersal. In North America, where a history of reticulate evolution via allopolyploid hybridization has long been suspected, nine plastid and two nuclear markers provide the first molecular support for a hypothesis explaining the parentage of five allopolyploid species that invokes a missing diploid ancestor as one of the progenitors. Field and common-garden experiments on correlated evolution of morphological and physiological traits found little support for light availability as the primary variable driving adaptive evolution in this group. This work develops Dryopteris as a model for investigating numerous systematic and physiological questions in ferns, and suggests several interesting avenues for future research. |
