VittadiniaRich. and TetramolopiumCass. (Asteraceae; Astereae) are two Austral-Pacific genera that have long been recognized as being closely related, having been variously merged and segregated by different authors. The two genera encompass diverse morphologies as well as broad and unusual distributional patterns. A number of other genera in the region have also been implicated as being related. We present the results of a reassessment of the phylogenetic relationships within the Pacific taxa of Tetramolopiumand among the Austral-Pacific Vittadinia-Tetramolopiumgroup of genera using molecular and morphological data. Morphological and ITS (internal transcribe spacer) sequence data for 40 species of Camptacra, Kippistia, Minuria, Peripleura, Tetramolopium, and Vittadinia, as well as one semi-herbaceous species of Australian Olearia, were subjected to cladistic analysis, separately and together. Results show both datasets exhibit marked homoplasy indicating why generic delimitation in the group has been historically problematic. This homoplasy may be the result of past intergeneric hybridization and/or convergence/parallelism among the taxa in similar arid environments in Australia. Minuria, Peripleuraand Tetramolopiumare paraphyletic as currently defined. Tetramolopium vagansfrom Australia appears to represent an undescribed genus. Kippistia suadefoliaand Peripleura diffusafall within the affinity group of Minuriaspecies. Vittadiniaand the remaining species of Tetramolopiumand Peripleuraform a strong affinity group. The distribution of indels and the combined analysis each provide evidence that the Hawaiian and Cook Island species of Tetramolopiumare descended from New Guinea species. The combined analysis also suggests that the Cook Island species is sister to the Hawaiian clade. Olearia argutashows no close affinity with either of the arborescent species of Oleariaused to root these analyses. Further studies are needed to clarify the relationships of other taxa (particularly in New Guinea) not included in this study that have been linked to the Vittadinia-Tetramolopiumgroup.

Key words: Asteraceae, ITS, morphology, phylogeny, Tetramolopium, Vittadinia