Allozyme diversity ofPittosporum (Pittosporaceae) on the Bonin (Ogasawara) Islands

The genusPittosporum includes about 160 species. Four species ofPittosporum occur in the Bonin Islands, and all of these are endemic to the islands. Electrophoretic studies of the four endemic species,P. tobira, from the Japanese mainland, andP. lutchuense var.denudatum from the Ryukyu Islands, were used to determine the origin and speciation pattern of the endemic species. 259 individuals were sampled from ten populations. Twenty loci in nine enzyme systems were resolved and used to calculate the gene frequencies for each population. A low genetic diversity was observed in three of the Bonin Island species, as is reported for other oceanic island plants. The exception,P. boninense, has the largest population size and widest distribution. A dendrogram generated by the UPGMA method shows two clusters. One consists of only the Bonin endemics, suggesting a monophyletic origin for these species.