There are suspected to be over 80 “congeners” of microcystin toxins, which all have a similar 7-peptide sequence that can differ at two positions. The congeners are identified with the call letters for the amino acids at those positions: Microcystin-LR is leucine/arginine, LA is leucine/alanine, RR is arginine/arginine, and so forth. If you’re not a scientist, think of these as different “flavors” of microcystin. LR has long held the title of the most commonly occurring microcystin congener globally (vanilla?).