The Tetratheca hirsuta Lindl. species complex from south-west Western Australia is one of the last unresolved complexes in this Australian endemic genus, and comprises the highly variable T. hirsuta, two rare, phrase-named taxa, and the closely allied T. hispidissima Steetz. An integrative approach, incorporating multivariate morphometric analysis and molecular phylogenetic and phenetic analyses of nrDNA (ETS) and cpDNA (ndhF–trnL, rpl16, trnS–trnG5ʹ2S), was used to investigate taxonomic boundaries within the complex. Morphological data showed clear divergence within the complex, and allowed several taxonomically uncertain individuals to be assigned. Phenetic and phylogenetic analyses of ETS showed substantial congruence with morphology, indicating that the groups recognised through morphometric analyses are also genetically divergent. By comparison, the chloroplast regions yielded incongruent gene trees, perhaps owing to incomplete lineage sorting, hybridisation or slow evolution of cpDNA. The present results support the recognition of the following four taxa: a morphologically and geographically expanded T. hispidissima, which is highly divergent from the remainder of the complex, and a closer grouping of T. hirsuta subsp. boonanarring Joyce & R.Butcher subsp. nov., T. hirsuta subsp. viminea (Lindl.) Joyce comb. et stat. nov. and T. hirsuta subsp. hirsuta.