provide evidence that Alphaproteobacteria have branched off later than most other phyla and classes of Bacteria except Betaproteobacteria and Gammaproteobacteria.

Other phylogenetic debates turn on the placement of Magnetococcidae and the protomitochondrion. There are some debates for the inclusion of Magnetococcidae in Alphaproteobacteria. For example, an independent proteobacterial class ("Candidatus Etaproteobacteria") for Magnetococcidae has been