Sabatia (Gentianaceae) contains ca. 20 species, distributed mainly on the U. S. A. Gulf and Atlantic Coastal Plains. Our aims were to determine 1) phylogenetic relationships among Sabatia species, 2) the time and place of Sabatia's origin and main areas of diversification, 3) relationships among sympatric species, and 4) how morphological and karyological characters evolved. We sequenced five noncoding cpDNA regions and nrITS for 30 accessions of Sabatia, Gyrandra, and Eustoma. Parsimony, likelihood, and Bayesian phylogenetic analyses were performed. Bayesian dating was done on a reduced-taxon, combined molecular dataset. The maximum clade credibility chronogram was used for ancestral area reconstruction and character optimization. Correlations between distributional, environmental and phylogenetic matrices were tested with spatial analyses. Phylogenetic analyses reveal that a Sabatia Gyrandra clade diverged in the late Middle Miocene, with Sabatia subsequently splitting into western and eastern Gulf Coast clades during the early Late Miocene. Further diversification took place in the Late Miocene-Pliocene, with more recent range expansion. Pliocene glacial/interglacial periods could have triggered range contraction/ expansion, associated with chromosomal changes. Closely related species of Sabatia tend to share both distributions and habitat types. Character optimization showed potential synapomorphies for a polymerous clade and a white-flowered clade.
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Vol. 40 • No. 3