prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Archaea" Woese et al. 1990
     Phylum "Euryarchaeota" Garrity and Holt 2001
       Class Methanobacteria Boone 2002 [monotypic]
         Order Methanobacteriales Balch and Wolfe 1981
           Family Methanobacteriaceae Barker 1956 (Approved Lists 1980)
             Genus Methanobacterium Kluyver and van Niel 1936 (Approved Lists 1980)