The Mitochondrial nad2 Gene as a Novel Marker Locus for Phylogenetic Analysis of Early Land Plants: A Comparative Analysis in Mosses

Abstract

The mitochondrial nad2 gene is established as a novel marker locus for phylogenetic analyses among early land plants. The potential of this gene for phylogenetic resolution was checked with a broad taxon sampling of 42 mosses (Bryopsida, including the enigmatic genus Takakia) to allow both a comparative analysis with the recently explored nad5 gene and the fusion of independent data sets. The mitochondrial gene sequences provide valuable phylogenetic information on the relationships of classically defined orders and their respective monophylies. The more rapidly diverging sequences of a group I intron in nad5 and of a group II intron in nad2 add information for fine resolution. Although both genes provide phylogenetic information in the same taxonomic range (above family level), the combined sequence alignment results in an approximate doubling in the number of nodes with significant bootstrap support (>90). According to our data, Buxbaumiales are a paraphyletic taxon in a key position between the earliest branching taxa (Sphagnales, Takakiales, Andreaeales, Polytrichales, and Tetraphidales) and all other orders, possibly to be placed in the subclass Bryidae. A dichotomy in the latter recalls two previously suggested superorders Hypnanae and Dicrananae. Both genes independently question the monophyly of the orders Dicranales and Neckerales and reject the inclusion of the genera Schistostega, Timmia, and Encalypta among Eubryales.