(Vol. 02, 1999-12) Taxonomy and Phylogeny of a Gulf Coast Disjunct Group of Spigelia (Loganiaceae Sensu Lato)
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We reconstructed phylogenies of populations of three closely related species of Spigelia (Loganiaceae sensu la to) to test hypotheses about relationships and taxonomic boundaries. The species studied occur in the southeastern U.S. with a disjunction in their distribution along the Gulf Coastal plain between Florida and Texas. Two sets of data, restriction sites of cpDNA and ITS sequences, were analyzed. We found three well-supported clades of cpDNA types that correspond to previous species delimitations, and the cpDNA clades representing the two Texas species were most closely related. This pattern of relationships was unexpected based on strong morphological similarities between the coastal plain Texas taxon, S. texana, and the Florida taxon, S. loganioides. Phylogenetic hypotheses based on ITS sequences were not strongly supported because there were few informative changes among the sequences, and therefore a combined analysis recovered similar topologies as with the cpDNA data alone. The distributional pattern in this group of Spigelia was compared to that of other groups of organisms in the Gulf Coast region in an effort to find similarities that may indicate a shared geological history.