Melophorus hirsutipes Heterick, Castanelli & Shattuck is a recently described taxon that was presented as occurring throughout most of mainland Australia and showing highly variable morphology. One highly variable character is sculpture, which is smooth and shiny in the type specimen but conspicuously scabrid and even rugulose in other forms. The scabrid and rugulose forms occur primarily in the monsoonal (seasonal) tropics of the northern third of the continent, a region that has recently been shown to be a global centre of ant diversity, but largely unrecognized as such because the great majority of species are undescribed. Here, we provide an integrated morphological, genetic (CO1) and distributional analysis of diversity within the scabrid and rugulose forms of M. ‘hirsutipes’. We recognize 16 species among the 56 scabrid/rugulose specimens sequenced, along with four shiny or shagreenate species that are embedded within them. We conclude that Melophorus ‘hirsutipes’ is a highly diverse group of at least 30 species given the very patchy geographical coverage of sequenced specimens. Our findings provide further evidence that the total number of species in monsoonal Australia is likely in the several thousands, which would make it the world’s richest known region for ant species.