The endemic Hawaiian Alsinoideae genera Schiedea and Alsinidendron (Caryophyllaceae) comprise the fifth largest radiation of flowering plants in the Hawaiian Islands, and one of the most diverse lineages in terms of morphology, habit, breeding system and habitat preference. The Hawaiian Alsinoideae have served as a model system for studying shifts from hermaphroditism to dimorphic breeding systems (dioecy, subdioecy and gynodioecy). Because of the possibility that habitat shifts have led to the evolution of dimorphism, the Hawaiian Alsinoideae may provide information on causal mechanisms underlying the evolution of sexual dimorphism. Despite the importance of phylogenetic approaches for understanding the relationship of habitat and breeding system evolution, recent phylogenetic analyses have failed to identify the closest relatives of the Hawaiian clade, confounding questions of monophyly, character state polarization and ancestral breeding system state reconstruction. Relationships within the Hawaiian Alsinoideae have remained unresolved, due, in part, to low genetic divergences among closely related species, and extremely rapid radiation following colonization of the Hawaiian Islands. In this study, we combine three data partitions (nr ITS and ETS sequences and morphology) for reconstructing phylogenetic relationships using maximum parsimony and maximum likelihood. Our results suggest 1) the Hawaiian Alsinoideae are strongly supported as monophyletic; 2) Schiedea is paraphyletic with Alsinidendron derived within a lineage containing S. verticillata from Nihoa; 3) S. membranacea and S. helleri comprise the sister clade to all other members of the lineage in Hawaii; 4) two primarily dimorphic clades identified in morphological analyses (adamantis and globosa clades) form a single clade in analyses based on all three data partitions, suggesting a single origin of dimorphic breeding systems in Hawaiian Alsinoideae. Analyses based on nucleotide partitions alone support two separate origins of dimorphism.

Key words: Alsinidendron , breeding systems, Caryophyllaceae, habitat shifts, Hawaiian islands, Schiedea