Cyanobacterial tree including all 16S rRNA gene copies. Cyanobacterial tree including all 16S rRNA copies, reconstructed using Bayesian analysis. Posterior probabilities >0.90 are displayed on the nodes. Colors indicate species-groups according to differentiation level. Species in yellow boxes control gene expression only via a circadian rhythm. Genus Trichodesmium shown in a green box is able to produce temporarily differentiated cells, called ‘diacocytes’. Multicellular species able to form terminally differentiated cells are shown in blue boxes. The letter “R” denotes gene copies that are positioned on the reverse DNA strand. Multicellular, terminally differentiated cyanobacteria are the only species exhibiting four copy numbers. Regardless of morphology, 16S rRNA sequences are highly conserved within each genome.