Network tree visualization of the supergroups. Network tree generated from the presence/absence matrix of 1,739 FSFs in 200 proteomes sampled equally from the four supergroups. The number of non-constant sites was 1,581. Nodes in the network tree are proteomes and are represented by rectangles labelled red, blue, green, and black for viruses, Archaea, Bacteria and Eukarya, respectively. Numbers on the major splits indicate bootstrap values.