Tetramolopium is a genus of sub-shrubs with an Australasian-Polynesian distribution. The Hawaiian and Cook Islands species represent a monophyletic group of three clades, each recognized by morphological and ecological characteristics and hypothesized to represent products of adaptive radiation. The genetic diversity of this group was assessed using RAPD and isozyme genetic markers, and compared with a previous nuclear RFLP analysis of 38 loci. This report represents the first study using these three markers in island plants. Twenty isozyme loci and 126 RAPD markers were surveyed for known populations. Overall diversity is very low (<0.22), following the general pattern observed in insular species, and confirming the extremely low diversity for Tetramolopium in comparison to all other studies. RFLP and RAPD marker diversity is similar while allozyme diversity is markedly lower. There is greater differentiation among species within sections than among sections. Analyses of all three marker sets do not agree with morphology/ecology based clades. The coefficient of genetic differentiation (Gst) over all species ranges from 0.558 for RFLP to 0.787 for allozymes and 0.858 in the RAPD data, indicating a high degree of genetic differentiation among species. The results show that allozyme data underestimate the total amount of genetic diversity present. The high Gst values are what would be expected as a result of genetic drift in small isolated insular populations. The low overall genetic diversity coupled with the lack of congruence between the morphological and genetic differentiation firmly establishes that the group has undergone recent and rapid adaptive radiation. These results suggest that conservation efforts in this genus need to focus on preserving all species since they each harbor a distinct set of genetic diversity.

Key words: genetic diversity, island biology, isozyme, RAPD, RFLP, Tetramolopium