Figure 2. Universal phylogenetic tree based on comparative sequence data from 16S or 18S ribosomal RNA (modified from Madigan et al., 1997). Colors highlight three domains of life (Archaea, Bacteria, and Eukarya). Evolutionary distances between groups are proportional to branch length (from tip to branch node). Hyperthermophilic species (those that only grow at >80 °C) are represented by red. Anoxygenic photosynthetic species are lavender. Oxygenic photosynthetic species are green. Note that chloroplasts group with cyanobacteria, indicating that genes for oxygenic photosynthesis were transferred to Eukarya through development of endosymbioses with cyanobacteria.