Phylogenetic analysis of Dryopteridaceae based on chloroplast rbcL sequences

Dryopteridoid ferns are distributed all over the world, but China and its adjacent regions have the highest species diversity, so China is a key region to study their phylogenetic relationships and evolutionary history. In this study, chloroplast rbcL sequences from 105 species of Dryopteridaceae and their relative lineages were used to reconstruct the phylogenetic trees using the MEGA2 and MrBayes 3.0b4 software. The phylogenetic relationships were inferred using the neighbor-joining, maximum-parsimony and Bayesian analysis, and three methods produced trees with largely congruent topology. These trees reveal that: (1) the species of the Dryopteridaceae in the classification of Ching except for those in Cyclopeltis are divided into two monophyletic groups corresponding to the two tribes, Dryopterideae Ching and Polysticheae Ching, but the genus Lithostegia should be transferred from Polysticheae to Dryopterideae, and the scopes of the two tribes should be extended: the tribe Dryopterideae includes the family Peranemaceae and some species of Ctenitis (a genus of the family Tectariaceae in Ching's classification), and the tribe Polysticheae includes the American Phanerophlebia and Polystichopsis; (2) Cyclopeltis is isolated from all the other species of Dryopteridaceae and their relative lineages; (3) the family Peranemaceae in Ching's classification may not be a natural group, and should be included in tribe Dryopterideae, and is closely related to Nothoperanema; (4) Cyrtomium and Polystichum are both resolved as paraphyletic, and Dryopteris polyphyletic; (5) Phanerophlebiopsis, Leptorumohra and Lithostegia are closely related to Arachniodes; Cyrtogonellum and some species of Polystichum and of Cyrtomium form a clade; Nothoperanema are closely related to Peranemaceae and some species of Dryopteris. The relationships among genera of Dryopteridaceae, the relationship between Peranemaceae and Dryopteridaceae, and that between Ctenitis and Dryopteridaceae, and the systemic positions of the genera endemic to China or Asia (Cyclopeltis, Nothoperanema, Phanerophlebiopsis, Leptorumohra, Lithostegia and Cyrtogonellum) are also discussed. Our phylogenetic analyses are based on only rbcL sequence data, so the results should be further confirmed using other lines of evidence.