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

Comparative restriction site mapping of the chloroplast genome of 26 accessions of Acacia plus outgroups (Caesalpinia, Albizia, and Ebenopsis) was carried out to analyze phylogenetic relationships among the subgenera of Acacia 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 subgenus Acacia were included in the analysis to generate hypotheses of the evolution and radiation of this group. Restriction maps constructed from data from 11 restriction enzymes yielded 212 informative restriction site out of a total of 900. Parsimony analysis resulted in a total of 12 most parsimonious trees of 663 steps each. The strict consensus tree and bootstrap and decay indices indicate strong support for monophyly Acacia subgenus Acacia and provisional support for the paraphyly of Acacia overall. Moderately 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-acacias and the more xerically adapted A. farnesiana species-group. A group of Caribbean species was found to be ancestral in Acacia subgenus Acacia and African and South American species were found to be relatively derived with respect to North American species, lending support to a Boreotropical, rather than a Gondwanan, hypothesis of the historical biogeography of Acacia subgenus Acacia.