WEEKS, ANDREA*, LEAH LARKIN, and BERYL B. SIMPSON. Integrative Biology and the Plant Resources Center, The University of Texas, Austin, Texas 78712. - A chloroplast DNA molecular study of the phylogenetic relationships of members of the Caesalpinia group (Caesalpinieae: Caesalpinioideae: Fabaceae).
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