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Recent studies investigating the evolution of genome size diversity in ferns have shown that they have a distinctive genome profile compared with other land plants. Ferns are typically characterized by possessing medium‐sized genomes, although a few lineages have evolved very large genomes. Ferns are different from other vascular plant lineages as they are the only group to show evidence for a correlation between genome size and chromosome number. In this study, we aim to explore whether the evolution of fern genome sizes is not only shaped by chromosome number changes arising from polyploidy but also by constraints on the average amount of DNA per chromosome. We selected the genus Asplenium L. as a model genus to study the question because of the unique combination of a highly conserved base chromosome number and a high frequency of polyploidy. New genome size data for Asplenium taxa were combined with existing data and analyzed within a phylogenetic framework. Genome size varied substantially between diploid species, resulting in overlapping genome sizes among diploid and tetraploid spleenworts. The observed additive pattern indicates the absence of genome downsizing following polyploidy. The genome size of diploids varied non‐randomly and we found evidence for clade‐specific trends towards larger or smaller genomes. The 578‐fold range of fern genome sizes have arisen not only from repeated cycles of polyploidy but also through clade‐specific constraints governing accumulation and/or elimination of DNA. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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]