Gaura is a small genus found in southern Canada, eastern and central United States, Mexico and Guatemala. Its center of distribution is within Texas. Raven and Gregory's monograph of the genus (1972) formed the basis for a cladistic analysis by Carr, Crisci and Hoch in 1990. In these treatments the 21 species of Gaura were assigned to eight sections. Four of these sections, (Campogaura, Gauridium, Schizocarya, Xenogaura) were monotypic. The remaining four sections (Gaura, Pterogaura, Stipogaura, Xerogaura) encompassed 17 species. In the cladistic analysis by Carr et al., section Gauridium is sister to the other seven sections within the genus, and the sections Xerogaura and Gaura are not monophyletic. We compared this morphologically-based phylogeny to one based on DNA sequence data from the nuclear ribosomal internal transcribed spacer region (ITS). A total of four outgroup taxa and 18 species of Gaura were included in this analysis. Our molecular phylogeny of Gaura supports five of the sections proposed by Raven & Gregory (Campogaura, Pterogaura, Schizocarya, Stipogaura, and Xerogaura), but the remaining three sections are problematic. Section Xenogaura is embedded within section Gaura, and the status of section Gauridium is uncertain. Our results indicate that this section is either sister to section Gaura or should be included within it. Thus, Gaura mutabilis, the sole representative of section Gauridium, may actually be one of the more derived species within Gaura and not the most basal member of the genus as suggested by Carr et al.

Key words: Gaura, ITS, molecular systematics, Onagraceae, phylogeny