Domain Bacteria Woese et al. 1990
   Phylum Cyanobacteria (ex Stanier 1974) Cavalier-Smith 2002 - cyanobacteria
     Class "Cyanobacteria" Cavalier-Smith, 2002
       Subsection IV
         Subgroup I see Family I
           Form genus Nostoc Vaucher ex Bornet & Flahault (1888)