The genus Annwoodia was named in 2017 to circumscribe an organism previously described as a member of the genus Thiobacillus, Thiobacillus aquaesulis - the type and only species is Annwoodia aquaesulis, which was isolated from the geothermal waters of the Roman Baths in the city of Bath in the United Kingdom by Ann P. Wood and Donovan P. Kelly of the University of Warwick - the genus was subsequently named to honour Wood's contribution to microbiology. The genus falls within the family along with Thiobacillus and , both of which comprise autotrophic organisms dependent on thiosulfate, other sulfur oxyanions and sulfide as electron donors for growth. Whilst Annwoodia spp. and spp. are thermophilic, Thiobacillus spp. are mesophilic.