 Furthermore, it has been found that the GC-content of ribosomal RNA (the traditional phylogenetic marker for prokaryotes) little reflects the GC-content of the genome.One example of this atypical decorrelation of ribosomal GC-content with phylogeny is that members of the "Holosporales" have a much higher ribosomal GC-content than members of the "Pelagibacterales" and "Rickettsiales", even though they are more closely related to species with high genomic GC-contents than to members of the latter two orders.The Class "Alphaproteobacteria" is divided into three subclasses "Magnetococcidae", "Rickettsidae" and "Caulobacteridae".