Iridomyrmex Mayr is Australia’s most ecologically dominant ant genus and has been estimated to contain at least 350 species. However, a recent taxonomic revision of the genus recognized only 79 species. Such contrasting views have major implications for an understanding of not only the diversity of such an important genus, but also its biogeography and evolutionary history. The taxonomic revision considered I. anceps (Roger) to represent a single species, despite its marked morphological variation and range from Australia to India and China. Subsequently, a preliminary morphological analysis recognized six species within the complex. Here we describe results from an integrated morphological, CO1 and distributional analysis that assesses if the six morphologically based taxa are differentiated genetically, and if there are additional species in the complex that are yet to be recognized. We found the morphological differentiation within the complex to be matched by extensive genetic divergence, and that matched morphological and genetic differentiation frequently occurs in sympatry. We recognize up to 18 species among our sequenced specimens from the complex, with their centre of diversity occurring in Queensland. Our findings are consistent with results showing that other Iridomyrmex species recognized in the taxonomic revision represent several to many actual species. The recognition of only 79 species of Iridomyrmex does not reflect true diversity within this ecologically dominant genus, nor the complexity of its biogeography and evolutionary history.