TOWARD A PHYLOGENY OF MIMOSA (LEGUMINOSAE: MIMOSOIDAE): A PRELIMINARY ANALYSIS OF SOUTHERN SOUTH AMERICAN SPECIES BASED ON CHLOROPLAST DNA SEQUENCE

The pantropical and subpantropical genus Mimosa L. comprises more than 500 species, of which nearly 480 are reported for the American Continent. Mimosa is subdivided into five sections, four of which are represented in southern South America: Botocaulon DC. Habbasia Dc. Calothamnos Barneby, and Alimosa. Previous taxonimic studies of the species from the austral region have found classification conflicts among (a) sections Batocanlon and Habbasia, (b) sections Calothamnos and Mimosa, and (c) series and subseries within section Mimosa. This paper reports a preliminary phylogenetic analysis of chloroplast nucleotide sequences of the lmL intron and the lmL-lmF intergenic spacer from 34 species of Mimosa and related genera. Key morphological characters were mapped onto the phylogenetic hypothesis and discussed. Sequence analysis indicates that the genus Mimosa is monophyletic; it is derived from Piptadenia riridiflora (Kunth) Benth. The four sections proposed by Barneby are not natural groups. The cladogram retrieved indicates that the representatives of Mimosa seet. Batocaulon are not clustered, the xerophylous represnetatives of this section are basal, and the remaining species are related to those species of section Habbasia, suggesting that section Batocaulon ser. Stipellares is more recently derived. The species of Mimosa sect. Calothamnos that were analyzed are nestd in section Mimosa. The results seem to support retention of this section within section mimosa as was noted previously by Bentham. The chloroplast sequence data suggest that the representatives from sections Calothamnos and Mimosa share a common ancestor with those from section Habbasia and section Batocaulon sex. Stipellures.