procaryotes
   Domain Archaea Woese et al. 1990 stat. inval. see Domain Archaea Woese et al. 2024
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Thermoplasmata Reysenbach 2001 nom. inval. [monotypic] see Class Thermoplasmata Reysenbach 2002
         Order Thermoplasmatalesᵀ Reysenbach 2001 nom. inval. see Order Thermoplasmatales Reysenbach 2002
           Family Picrophilaceae Schleper et al. 1996 [monotypic]
             Genus Picrophilusᵀ Schleper et al. 1996