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The genome evolution of ferns has been considered to be relatively static compared with angiosperms. In this study, we analyse genome size data and chromosome numbers in a phylogenetic framework to explore three hypotheses: the correlation of genome size and chromosome number, the origin of modern ferns from ancestors with high chromosome numbers, and the occurrence of several whole-genome duplications during the evolution of ferns. To achieve this, we generated new genome size data, increasing the percentage of fern species with genome sizes estimated to 2.8% of extant diversity, and ensuring a comprehensive phylogenetic coverage including at least three species from each fern order. Genome size was correlated with chromosome number across all ferns despite some substantial variation in both traits. We observed a trend towards conservation of the amount of DNA per chromosome, although Osmundaceae and Psilotaceae have substantially larger chromosomes. Reconstruction of the ancestral genome traits suggested that the earliest ferns were already characterized by possessing high chromosome numbers and that the earliest divergences in ferns were correlated with substantial karyological changes. Evidence for repeated whole-genome duplications was found across the phylogeny. Fern genomes tend to evolve slowly, albeit genome rearrangements occur in some clades., (© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.)

The origin of the latitudinal biodiversity gradient has been studied using various approaches. Here, we employ a comparative phylogenetic approach to infer evidence for the hypothesis that differences in diversification rates are one of the main factors contributing to the assembly of this gradient. We infer the phylogeny of the two sister genera Phegopteris and Pseudophegopteris. The two genera are distinct in their species richness (4 vs. 20 spp.) and their preferences to temperate to subtropical ( Phegopteris) or tropical climates ( Pseudophegopteris). Using sequences of three plastid DNA regions, we confirm the monophyly of each genus and infer the inter- and intra-generic phylogenetic differentiation of the sister clades. We recover evidence for distinct net-diversification rate between the two genera, which may be caused either by a higher extinction risk of temperate Phegopteris or a higher speciation rate of tropical Pseudophegopteris. We discuss our results in the context of our current knowledge on the speciation processes of ferns. We conclude on the crucial influence of other factors such as the rise of the Himalaya on the diversification of these ferns. [ABSTRACT FROM AUTHOR]