Synechocystis is a genus of unicellular, freshwater cyanobacteria in the family Merismopediaceae.

PCC 6803, which is a well studied model organism.

Like all cyanobacteria, Synechocystis branches on the evolutionary tree from its ancestral root, Gloeobacter violaceus.

[2] Synechocystis is not diazotrophic, and is closely related to another model organism, Cyanothece ATCC 51442.

[3] It has been suggested that originally Synechocystis possessed the ability to fix atmospheric nitrogen, but lost the genes required for the process.