A total-evidence phylogeny of the lady fern genus Athyrium Roth (Athyriaceae) with a new infrageneric classification.

The lady fern genus Athyrium represents one of the most diversified lineages in Athyriaceae with about 160-220 known species, and is notorious for its taxonomic difficulty. Despite progress in recent phylogenetic studies involving this genus, it still lacks a modern systematic and taxonomic update using integrative analyses of molecular and morphological evidence based on a broad species sampling. Here, we present, to our knowledge, the most comprehensive phylogenetic analysis of the genus to date based on a total-evidence approach, covering all formerly accepted segregates within the athyrioid ferns. We sampled up to eight plastid markers and 20 morphological characters for each species. Our analyses, including maximum parsimony, maximum likelihood and Bayesian inference, yield a robust phylogenetic framework. We find that Athyrium is not monophyletic by recovering Athyrium skinneri and A. alpestre nested with Anisocampium and Cornopteris respectively while Pseudocystopteris is included in Athyrium. Furthermore, eight well-resolved clades and two isolated species within Athyrium are found in the phylogenetic topology, which can be also characterized by morphological synapomorphies from traits of petioles, leaves, sori and spores. In the interest of recognizing monophyletic taxa with morphological synapomorphies, we agree with the inclusion of Pseudocystopteris in Athyrium as proposed in previous studies, but treat Anisocampium and Cornopteris as separate genera. We further propose to resurrect a monotypic Pseudathyrium to accommodate A. alpestre. Based on morphological characters and molecular phylogeny, a new infrageneric classification system of Athyrium is proposed which subdivided it into ten sections, and one New-World species A. skinneri is transferred into Anisocampium.