A molecular phylogeny of selligueoid ferns (Polypodiaceae): Implications for a natural delimitation despite homoplasy and rapid radiation

Homoplasy, autapomorphy and rapid radiation have frequently been discussed as the main causes of instable generic classifications of plants including ferns. In this study, we explore the natural generic classification for selligueoid ferns by investigating the phylogenetic relationships among almost all its previously recognized segregates. We compare the phylogenies that resulted from two datasets. Dataset 1 comprises a broad taxonomic sampling of fifty-one species of selligueoid ferns. Phylogenetic analysis of this dataset revealed a notable long branch followed by a polytomy recovering three core clades of selligueoid ferns. Only one of the core clades corresponds to the traditional generic concept of Arthromeris. Dataset 2 includes fewer species but a broader sample of six plastid DNA markers. However, the results of this dataset show that the increase of informative molecular characters still did not provide sufficient evidence to resolve the polytomy. The long branches together with a consistent backbone polytomy support a rapid radiation in the selligueoid ferns. The majority of morphological characters were recovered as homoplastic, which hampers the identification of segregates with unambiguous diagnostic characters. Considering morphological characters and our molecular phylogeny, a single genus Selliguea s.l., which includes all selligueoid species, is proposed here to achieve taxonomic stability in this group.