procaryotes
   Domain Archaea Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Methanobacteria Boone 2001 nom. inval. see Class Methanobacteria Boone 2002
         Order Methanobacteriales Balch and Wolfe 1981
           Family Methanobacteriaceae Barker 1956 (Approved Lists 1980)
             1 Genus Methanobacterium Kluyver and van Niel 1936 (Approved Lists 1980)
             2 Genus Methanobrevibacter Balch and Wolfe 1981
             3 Genus Methanosphaera Miller and Wolin 1985
             4 Genus Methanothermobacter Wasserfallen et al. 2000