Species Relationships in Krameria (Krameriaceae) Based on ITS Sequences and Morphology: Implications for Character Utility and Biogeography

The Krameriaceae is a monotypic family of 18 species distributed in the warm arid and semiarid regions of North and South America. We have used sequence data from the internal transcribed spacer region of the nuclear ribosomal DNA repeat (ITS 1, 5.8S, and ITS 2) and morphology to infer relationships within Krameria. Using Kallstroemia parviflora, Guaiacum angustifolium, and Tribulus terrestris, three North American members of the Zygophyllaceae, as out groups, our data provide evidence for two major clades in the genus, each containing a North and a South American subclade. Both the major clades and subclades are supported by morphological synapomorphies. The phylogeny does not provide an unequivocal resolution as to the hemisphere in which Krameria arose, but it does indicate an initial split leading to the ancestors of the two clades, each of which subsequently produced radiations in North and South America. Therefore, there must have been two independent dispersals to, or two vicariant episodes involving, North and South America.