the systematics of i. tarsalis is far from being understood. morphological and molecular analyses have given contradictory results, pointing towards its inclusion or exclusion from the phyllotini. the karyotype of irenomys tarsalis, as well as its c-bands are reported for the first time. the species has 2n = 64 chromosomes (fn = 98) and a c-banding pattern characterized by small amounts of centromeric heterochromatin. although the high diploid number and the c-bands of i. tarsalis support the notion of the species′ ancestral karyotypic condition, its affiliation within the sigmodontines cannot be discerned by the data.