Gloeobacter violaceus is a distinctive cyanobacterium notable for lacking thylakoid membranes, placing all photosynthetic pigments directly in the cytoplasmic membrane unlike all other known cyanobacteria. It is found on moist calcareous rocks and cave walls, and its deep-branching position in cyanobacterial phylogenies makes it of great interest for understanding the evolution of photosynthesis. Its genome has been fully sequenced, revealing unique metabolic features.