The endemic Hawaiian genus Hesperomannia A. Gray was investigated to examine relationships among species and to test the hypotheses of dispersal to the Islands over 17 mya. Both nuclear internally transcribed spacer (ITS) sequences and random amplified polymorphic DNA (RAPD) markers were used to assess genetic divergence among populations and species. PAUP, Neighbor-Joining, and Bayesian phylogenetic trees were generated to examine species boundaries and relationships. Principal coordinates analysis was used to examine relationships among individuals within populations and genetic distances among populations. Analyses suggest that four species should be recognized: H. lydgatei, H. oahuensis, H. swezeyi, and H. arborescens. Sequence analysis is consistent with arrival to Hawai‘i as recently as the last 2.3 my, after the three main island groups (Kaua‘i, O‘ahu, and Maui Nui) had emerged, followed by rapid dispersal among them. O‘ahu species are more closely related to each other than either is to the species of Maui Nui as was previously hypothesized. In contrast, Maui Nui plants are not genetically distinct enough to warrant separate species as previously recognized. Long-distance dispersal is evoked for dispersal among distantly situated island groups, but there is no evidence that colonization followed the progression rule model of dispersal among the Islands and may have occurred from younger to older islands. Vicariance is probable within O‘ahu and among the islands of Maui Nui following erosion and subsidence of those islands, and may also explain distribution of species among O‘ahu and Maui Nui. A revised key to and diagnostic descriptions of the species of Hesperomannia are provided.