A maximum-likelihood distance tree for sequenced cyanobacteria based on concatenated sequences for 44 conserved proteins. The distance scale (bar = 0.1 substitutions per site) is shown in the top right hand corner. The tree was rooted using B. subtilis and S. aureus sequences. The numbers at the nodes indicate % of puzzling quartets supporting various nodes. The low B/A ecotype clade refers to the Prochlorococcus spp. containing lower ratio of chlorophyll b/a
that are adapted to growth at high light intensities.