Relationships within the tribe Caesalpinieae have proved problematic for over 200 years. The most recent treatment by Polhill placed the genera in this tribe in nine informal generic groups. Of these, the Caesalpinia group has proved to be particularly intractable because of the range of variation and apparent convergence in floral and fruit morphology. A morphological cladistic study by Lewis and Schrire indicated that the genus Caesalpinia was paraphyletic with all of the other genera currently placed in the Caesalpinia group included within Caesalpinia. We have used sequences from the trnL intron and trnL-trnF spacer regions to provide new insights into the phylogenetic relationships of these genera. Included in our study are representatives of most of the genera in the Caesalpinia group, numerous species of Caesalpinia itself, and various outgroups from Polhill’s other informal Caesalpinieae groups. While our sampling is limited, our data indicate that Polhill’s informal groups are monophyletic. Additionally, like Lewis and Schrire, we find that Caesalpinia is paraphyletic. However, our findings indicate very different relationships among the genera from those suggested using morphology. In particular, we find that Pomaria and Hoffmannseggia are not sister taxa and that South American genera such as Zuccagnia and Balsamocarpon are more closely related to Hoffmannseggia than Hoffmannseggia is to Pomaria.

Key words: Caesalpinia, Caesalpinieae, Fabaceae, trnL intron, trnL-trnF spacer