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
         1 Family Methanobacteriaceae Barker 1956 (Approved Lists 1980)
         2 Family Methanothermaceae Stetter 1982