Phylogenetic hypotheses generated from chloroplast DNA restriction site mapping and sequencing of the internal transcribed spacer (ITS) region of ribosomal DNA of Acacia subgenus Acacia from the New World and Africa indicate the importance of a group of species endemic to the West Indies as sister to the main radiation of the subgenus in the New World in North America. While the results of separate phylogenetic analyses differ in a number of important respects, the relatively basal position of the West Indian-endemic species (the Acacia acuifera species-group, an edaphically specialized and, for the most part, restricted endemic of serpentine and calcareous outcroppings) lends support for a boreotropical model of the historical biogeography of the subgenus. Other West Indian species not included in the Acacia acuifera species-group were found to share clades with mainland North, Central, and South American groups, lending support for a dispersalist model of the biogeography of these species. The results of the phylogenetic analyses indicate that Caribbean members of Acacia subgenus Acacia may display signal from early and later phases of the Caribbean flora. Weedy, widespread members in the Caribbean scarcely differentiated from mainland relatives may belong to a cohort of recently dispersed elements while the restricted serpentine- and calcareous-endemic members of the Acacia acuifera species-group, due to their relatively basal position within the subgenus and lack of any close relatives in mainland areas, may represent a relictual group having a relatively long history in the Caribbean. Their edaphic endemism may partially explain their ability to persist in the Caribbean as plants in these areas are likely to have been less prone to competitive exclusion by colonizing species.

Key words: Acacia , boreotropical, Fabaceae