Microcystis spp. have been known for their toxicity for some time although it was not until Botes et al. (1984) described the structure of "cyanoginosin-LA" from M. aeruginosa that more detailed analysis of this toxicity could be carried out. Since that time approximately 35 different microcystins have been described in Microcystis spp., primarily from M. aeruginosa and M. viridis.
Microcystis spp. are single-celled, colonial, freshwater cyanobacteria and have been identified world-wide. Although many studies have not been able to confirm the species, both M. aeruginosa and M. viridis appear to be the most common microcystin-prodcuing species.