The family Ferroplasmaceae (Golyshina et al. 2000, 1004VP) is one of the four families within the order Thermoplasmatales. It includes two genera, Ferroplasma and Acidiplasma; Ferroplasma is a monospecific genus with the only validly described species being Ferroplasma acidiphilum. The second genus within this family, Acidiplasma, is represented by two species, Acidiplasma aeolicum and Acidiplasma cupricumulans, initially described as Ferroplasma cupricumulans. Members of the family are cell wall-deficient, extremely acidophilic (optimal pH for the growth is 1–1.7), iron oxidizing, facultatively anaerobic, moderately thermophilic, and mesophilic organisms with certain differences in physiology and chemotaxonomy. The main polar lipids are glycosyl/galactosyl dibiphytanyl phosphoglycerol tetraethers. The DNA G + C content (mol%): 34–37. The members of the family Ferroplasmaceae inhabit acidic environments, such as sulfide ores, mines, drainage waters, and volcanic areas worldwide.