Species diversity and reticulate evolution in the Asplenium normale complex (Aspleniaceae) in China and adjacent areas

The Asplenium normale complex contains the widespread A. normale and several geographically restricted species: A. boreale, A. hobdyi, A. kiangsuense, A. oligophlebium and A. shimurae. The taxonomy of this group is unclear with some entities treated infraspecifically or as synonyms. Furthermore, the existence of diploids and tetraploids in this species complex is suggestive of reticulate evolution. In order to formulate a natural classification and to investigate the relationships in this complex, phylogenetic analyses of plastid and nuclear sequence data and inference of ploidy level were used to assess the distinctiveness of putative taxonomic units and their relationships. The Asplenium normale complex was recovered as a monophyletic group comprising six principal chloroplast lineages. The results support the hypothesis that A. normale s.l. contains several species. Based on our inferences, we outline an improved species classification recognizing three diploid and four tetraploid entities. Incongruence of chloroplast and nuclear phylogenies was interpreted to be a result of recurrent reticulation events in the A. normale complex.