Schiedea exhibits an extraordinary range of morphological diversity, breeding system variation, and habitat preference, making it among the most spectacular adaptive radiations in the Hawaiian Islands. We explored phylogenetic relationships of the endemic Hawaiian genus Schiedea (33 species) using combined molecular (nr ITS and ETS sequences) and morphological data. Schiedea is monophyletic and several natural groups can be recognized corresponding to six sections. Schiedea membranacea and S. helleri comprise a clade sister to the remaining species of Schiedea. Species of the formerly separate genus Alsinidendron are monophyletic and are treated as second and third well-marked sections. These taxa are weakly associated with Schiedea verticillata from Nihoa, treated as a fourth section. The fifth section includes 12 species characterized by large, one-nerved leaves. The sixth clade contains all species of two primarily dimorphic clades identified in previous morphological analyses (adamantis and globosa clades), suggesting a single origin of dimorphic breeding systems in Schiedea and several reversals to hermaphroditism. There have been at least two apparent shifts from mesic to dry habitats, one in the basal, morphologically divergent S. verticillata, and at least one other in the large clade containing primarily dimorphic species. The correlation of breeding system and wind pollination with dry habitats indicates that breeding systems may have evolved in response to shifts to dry habitats during the course of adaptive radiation. In contrast, shifts to wet habitats are associated with the evolution of autogamy, which occurs in eight species. The diversity of breeding systems is greater in Schiedea than any other monophyletic lineage in the Hawaiian Islands.

Key words: Caryophyllaceae, ETS, Hawaiian Islands, ITS, phylogeny, Schiedea