Homoplasy increases phylogenetic structure

According to currently accepted theories, rapidly evolving nucleotide sites are phylogenetically less informative than more slowly evolving ones, especially for recognizing more ancient groupings. For this reason third codon positions are often regarded as less reliable than first and second positions as indicators of phylogeny. Analysis of the largest nucleotide matrix treated to date - 2538 rbcL sequences covering all major lineages of green plants - shows the opposite: although rapidly evolving and highly homoplastic, third positions contain most of the phylogenetic structure in the data. Frequency of change should thus be used with caution as a criterion for weighting or selecting characters.