Implications of chloroplast DNA restriction site variation for systematicsof Acacia (Fabaceae : Mimosoideae)

Comparative restriction site mapping of the chloroplast genome of 26 access ions of Acacia plus outgroups (Caesalpinia, Albizia, and Ebenopsis) was car ried out to analyze phylogenetic relationships among the subgenera of Acaci a and, in particular, within Acacia subgenus Acacia. One or more taxa from each of seven New World species-groups plus two African species of Acacia s ubgenus Acacia were included in the analysis to generate hypotheses of the evolution and radiation of this group. Restriction maps constructed from da ta from 11 restriction enzymes yielded 212 informative restriction sites ou t of a total of 900. Parsimony analysis resulted in a total of 12 most pars imonious trees of 663 steps each. The strict consensus tree and bootstrap a nd decay indices indicate strong support for monophyly of Acacia subgenus A cacia and provisional support for the paraphyly of Acacia overall. Moderate ly to strongly supported clades within Acacia subgenus Acacia indicate that the mesically adapted A. macracantha species-group is polyphyletic and may represent lineages with sister group relationships with both the ant-acaci as and the more xerically adapted A. farnesiana species-group. A group of C aribbean species was found to be ancestral in Acacia subgenus Acacia and Af rican and South American species were found to be relatively derived with r espect to North American species, lending support to a Boreotropical, rathe r than a Gondwanan, hypothesis of the historical biogeography of Acacia sub genus Acacia.