Riboswitch distributions. The dimensions of each square are proportional to the frequency with which a given riboswitch occurs in the corresponding taxonomic group. A phylogenetic tree with the standard accepted branching order for each group of organisms is shown on the left. For bacteria, this tree is adapted from  with the addition of Fusobacteria . On the right is a graph depicting the total number of nucleotides from each taxonomic division in the sequence databases that were searched.