Procaryotic Genera
   Domain "Archaea" Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Methanobacteria Boone 2001 nom. inval. [monotypic] see Class Methanobacteria Boone 2002
         Order Methanobacterialesᵀ Balch and Wolfe 1981
           1 Family Methanobacteriaceae Barker 1956 (Approved Lists 1980)
           2 Family Methanothermaceae Stetter 1982 [monotypic]