Cyanobacteria, commonly known as blue-green algae, are members of the Kingdom Monera. Members of this kingdom lack a nuclear region clearly defined by a membrane or envelope and are thus known as prokaryotes. Members of the blue-green algae are among the oldest fossils ever found, dating back to over three billion years.

Cyanobacteria are photosynthetic unicellular or colonial algae. They contain chlorophyll a and other accessory pigments, but these are not located in distinct chloroplasts. Instead, they are distributed throughout the cell on flat organelles called thylakoids. Accessory pigments in this group include b- carotenes, xanthophylls, and phycobilins. One type of phycobilin is phycocyanin, which gives the characteristic bluish-green color, and hence their common name. Their cell wall is composed of mucopeptides. Many species also have a gelatinous sheath around their cells. Some species live as single-celled individuals like the genus Sphaerocystis, while others grow in colonies like...