The diagnostic characteristics and distinctiveness of plant taxa have traditionally been based on a combination of geographic and morphological discontinuity. Implicit within these concepts is the notion that morphological variation is fixed and that gene flow among taxa is limited. However, species complexes that comprise a range of more-or-less continuous morphotypes often confound such assumptions and resist formal taxonomic treatment. A range of independent data sources, namely, nucleotide sequences, volatile oils and traditional morphology, were used in an integrative approach to resolve the taxonomic structure within the geographically widespread species complex of Prostanthera lasianthos Labill. We concluded that no dataset has primacy in defining segregate taxa, and that a combination of morphological and molecular data was required to determine the taxa within. As a result, we amended the description of P. lasianthos sens. strict. and recognise the following five new segregate species: Prostanthera largiflorens B.J.Conn & K.Proft, P. lasiangustata J.Carrick ex B.J.Conn & K.Proft, P. rupicola B.J.Conn & K.Proft, P. subalpina B.J.Conn & K.Proft, and P. williamsii B.J.Conn & K.Proft.