Phylogenetic relationships among fern rust fungi and comb. nov.

The rust fungi () that infect ferns, early diverging vascular plants, are neither "primitive" nor monophyletic, as once hypothesized. The neotropical fern pathogen, (), specializes on species of . is believed to have evolved in a period ca. 211 mya, which is after the evolution of the temperate fern rust fungi that parasitize later diverged ferns. is the only rust species in the genus known to infect ferns, the majority of which infect flowering plants. In this study we examined multiple new and herbarium specimens of and reconstructed its phylogenetic history with data generated from the 28S nuclear rDNA repeat. is the sister species to another neotropical fern rust, (), which also infects early diverged leptosporangiate fern species, and the new combination is made. Interestingly, and differ primarily in sorus structure, i.e., subepidermal in the former vs. suprastomatal in the latter fungus. Characters such as suprastomatal sori and probasidia that germinate without dormancy are now known to represent a suite of adaptations that have been derived multiple times within , most likely in response to tropical climates.