Gloeomargarita lithophora

Gloeomargarita lithophora, a cyanobacterium, is the proposed closest present day relative of all chloroplasts (except for the independently evolved in the amoeboid Paulinella chromatophora). The ancient relative of Gloeomargarita's was engulfed by a eukaryotic host in an endosymbiotic event around 1900-1400 million years ago. The origin of plastids by endosymbiosis signifies the beginning of photosynthesis in eukaryotes, and as such their evolutionary relationship to Gloeomargarita lithophora, as the sister group, is of high importance to the evolutionary history of endosymbiotic organelles and photosynthesis.