Phylogenetic information in the mitochondrial nad5 gene of pteridophytes: RNA editing and intron sequences

A conserved coding region of the mitochondrial nad5 gene (1098-1107 bp of p rotein coding sequence) was amplified from 30 pteridophytes (26 ferns and 4 fern allies). A group II intron sequence conserved in all ferns except the eusporangiate genus Ophioglossum is also present in the whisk fern Psilotu m nudum and the lycopod Huperzia selago, but absent from the horsetails (Eq uisetum), the seed plants and the bryophytes. Phylogenetic trees constructe d with different methods consistently suggest several monophyletic units. T he conserved group II intron sequence provides valuable additional phylogen etic information. Leptosporangiate ferns are monophyletic with Osmunda as t he basal-most branching genus followed by Trichomanes, Matonia and Lygodium . These genera are set distantly apart from other leptosporangiate ferns, i ncluding the tree and water ferns, which branch in close proximity. Species of Polypodiaceae, Dryopteridaceae, Thelypteridaceae, Aspleniaceae and Blec hnaceae appear in a monophyletic crown group of derived leptosporangiate fe rns with Dryopteridaceae as a paraphyletic taxon. Placement of Psilotum in a class of its own receives no support from the mitochondrial sequences, wh ich rather suggest its inclusion among eusporangiate ferns (Ophioglossales) . RNA editing is required to correct the genetic information of the nad5 ge ne in all species investigated and includes the removal of stop codons from the reading frames. The influence of RNA editing on phylogenetic tree cons truction is investigated and discussed.