Mitochondrial insights for land plant phylogeny and a comparative case study in ferns

Molecular data have enormously contributed to identify several groups of land plants as monophyletic clades or, in other cases. to reject certain systematic concepts. Molecular phylogenetic research of plants is as yet dominated by investigations of chloroplast DNA. Plant mitochondrial DNA is more complex and structurally Much more variable in evolution. The occurrence of mitochondrial introns in particular differs among early land plant groups, but is highly stable among members of a given clade. Mitochondrial data strongly support it dichotomy between liverworts and all other land plants and furthermore Suggest serial sister group relationships of hornworts and mosses to the tracheophytes. The sequence variability in positionally conserved introns can be used for finer phylogenetic resolution within a clade, as was shown for the mosses. In another case, however, highly unequal rates and patterns of evolution make phylogenetic construction more difficult and an example for the phylogeny of ferns is discussed in comparison to three chloroplast loci and the nuclear 18S rRNA.