Xerolitor, a new, monotypic genus of fungus-growing ants, is described to accommodate the phylogenetically isolated, relict species Mycetosoritis explicatus Kempf. We also diagnose the male and the larva of Xerolitor explicatus (Kempf) comb.n. and report ecological observations for the species, including nest architecture and foraging behaviour. Xerolitor explicatus comb.n. inhabits the dry habitats of the Brazilian Cerrado and the Bolivian and Paraguayan Gran Chaco. Bayesian multilocus phylogenetic analyses indicate that X. explicatus comb.n. is, contrary to some prior hypotheses, a member of the higher' fungus-growing ants and the sister taxon of the genus Sericomyrmex Mayr. Results from phylogenetic analyses of the fungal cultivar grown by X. explicatus comb.n. in Paraguay, as well as the presence of gongylidia, indicate that the fungal mutualist is a member of the clade of higher fungal cultivar species and that it is probably the same species cultivated by some Trachymyrmex Forel and Sericomyrmex species.
