phormidium phormidium phormidium is a genus of cyanobacteria in the family oscillatoriaceae. phormidium scientific classification domain: bacteria phylum: cyanobacteria class: cyanophyceae order: oscillatoriales family: oscillatoriaceae genus: phormidiumkützing ex gomont, 1892 as a result of recent genetic analyses, several new genera were erected from this genus, e.g. potamolinea. species 83, including; phormidium aerugineo-caeruleum