Molecular phylogenetic analysis of the Hawaiian endemics Schiedea and Alsinidendron (Caryophyllaceae)

Schiedea and Alsinidendron (Caryophyllaceae), which represent the fifth or sixth largest endemic radiation of species in the angiosperm flora of the Hawaiian Islands, exhibit striking diversity in morphology, breeding system, and habitat. To gain a historical perspective on this diversity, we conducted a phylogenetic analysis using restriction site variation in chloroplast DNA and nuclear ribosomal DNA. In addition, we compared, and ultimately combined, the molecular data with a recently published morphological data set. Within the Schieden-Alsinidendron lineage, DNA variation is limited, and relationships are generally poorly resolved. These results raise the possibility that, following the initial colonization of the Hawaiian archipelago and the early diversification of the complex, much of the complex radiated rapidly and relatively recently. Phylogenetic analyses of DNA data revealed three clades within the complex (the S. membranacea, S. nuttallii, and S. adamantis clades), in agreement with results of a morphologically-based analysis. Molecular data do not, however, support the S. globosa clade, a weakly-supported clade based on morphology. A combined analysis of morphological and molecular data provided both greater resolution and stronger internal support than either data set did individually. The molecular and combined topologies suggest nearly identical patterns of the evolution of sexual dimorphism, habitat shifts, and biogeography within the complex. However, the greater resolution in trees derived from the combined analysis suggests simpler patterns of breeding-system evolution and habitat shifts. Sexual dimorphism may have evolved twice in the complex, with a single reversal to hermaphroditism in one species, or perhaps only once, with three reversals to hermaphroditism. Although the habitat occupied by the ancestor of the complex remains uncertain, it appears that a single shift to dry habitats more or less accompanied the evolution of dimorphic breeding systems, followed by a single shift back to a mesic environment in one species. Alternatively, two parallel shifts to dry habitats may have occurred. Molecular data are consistent with an origin on Kaua'i of the S. membranacea, S. adamantis, and S. nuttallii clades, as suggested by previous morphological analyses. However, both the molecular and combined trees suggest it is equally likely that the complex originated on O'ahu.