A Molecular Approach to the Phylogeny of Bryophytes: Cladistic Analysis of Chloroplast-Encoded

As the most primitive living lineages of embryophytes, bryophytes are critical to an understanding of the evolution of the land flora. A relatively robust phylogenetic hypothesis exists, based on morphology, ultrastructure, and chemistry, in which the classical group "bryophytes" is not monophyletic. Instead, the mosses seem to be more closely related to the tracheophytes than to the hornworts or liverworts. However, details of these relationships remain unclear. In this paper we explore the usefulness of comparative molecular studies as a potential source of independent data to test and refine this cladogram. We have generated preliminary nucleotide sequence data from portions of the 16S and 23S ribosomal RNA genes in the chloroplasts of 11 bryophytes selected from diverse groups. These data, even though they show considerable homoplasy, appear to be historically informative at this deep phylogenetic level since they support a cladogram that is identical to the morphological one. Future studies will expand the molecular comparisons by sequencing the rest of these two rRNA genes, as well as the protein-coding gene rbcL, for many more species.