CLARKE, H. DAVID. Dept. of Biology, CPO #2440, University of North Carolina at Asheville, Asheville, NC 28804. - Biogeography of Acacia subgenus Acacia in the Caribbean and neotropics based on ITS nrDNA sequences and cpDNA restriction site mapping.
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