Korarchaeota is a phylum of hyperthermophilic Archaea that branches closest to the archaeal root. The Korarchaeota were originally discovered by microbial community analysis of ribosomal RNA genes from environmental samples of a hot spring in Yellowstone National Park. No pure cultures from this phylum have been isolated yet, but the sequenced 16S ribosomal RNA genes belong to organisms that branch near the root of the archaeal phylogenetic tree. Stable enrichment mixed cultures, containing Korarchaeota identifiable by in situ hybridization, have been grown at thermophilic conditions in the laboratory.