procaryotes
   Domain Archaea Woese et al. 1990 stat. inval. see Domain Archaea Woese et al. 2024
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Methanobacteria Boone 2001 nom. inval. [monotypic] see Class Methanobacteria Boone 2002
         Order Methanobacterialesᵀ Balch and Wolfe 1981
           Family Methanothermaceae Stetter 1982 [monotypic]
             Genus Methanothermusᵀ Stetter 1982