Callirhoe comprises nine species and two varieties distributed from northeastern New Mexico through Florida including northeastern Mexico. The genus exhibits variation in sex expression possessing gynodioecy and monecy. Gynodioecy is rare in the Malvaceae yet three of the nine species of Callirhoe are gynodioecious and a fourth exhibits functional gynodioecy. Preliminary results of morphology and sequence data derived from the nrDNA ITS region, will be presented to examine the phylogenetic relationships of the taxa. Breeding system data will be mapped onto the species phylogeny to estimate the pathway of breeding system evolution in the genus.

Key words: Breeding system evolution, Callirhoe, Gynodioecy, ITS, Malvaceae, Phylogenetics