The monotypic genus Bontia, endemic to the Caribbean, is the extreme outlier of a primarily southern-hemisphere Old World family, the Myoporaceae. Ninety-five percent of the 250 species of Myoporaceae sensu R. J. Chinnock (in press) are endemic to Australia. Only six species in the family occur north of the equator; of these, all but Bontia daphnoides are locally distributed in the western Pacific. Is the evolutionary history of Bontia truly shared with Myoporaceae, or has it descended instead from the family's probable sister lineage, the Leucophylleae (Scrophulariaceae) of Mexico and Central America? We examined the possibility that Bontia is indeed an outlying member of the Myoporaceae by sequencing the rpl16 intron of the chloroplast genome for 60 taxa representing all major morphological lineages within the family, and representatives of probable outgroups that include the Leucophylleae. The sequence data were partitioned based on the probable secondary structure of the Group II intron; partition categories were defined as stem, loop, and interceding sequence. Relative rate of base change per partition was estimated using the method of Vawter and Brown (1993). The method does not assume rate constancy and allows for base composition bias between taxa and secondary structure components; therefore, relative rates of substitution can be compared between sequence partitions to study the amount of mutation occurring in stem, loop, and interceding sequence. We present the results of this partition study and the phylogeny estimate based on this data set. In this topology, Myoporaceae is monophyletic, Leucophylleae is sister to Myoporaceae, and Bontia is derived from within Myoporaceae. The results suggest that the distribution of Bontia is due to dispersal from an Australian ancestral lineage.

Key words: biogeography, data partitioning, methodology, Myoporaceae, noncoding sequences, secondary structure