Spatial-autocorrelation statistics indicate that flower color morphs at a locus controlling pink versus blue flowers (P/p) are clustered into patches in Ipomoea purpurea populations. For the P/p locus, the number of homozygous pink individuals within an average patch (patch size) is approximately equal for 12 populations having wide-ranging densities, as expected in a bee-pollinated plant with limited seed dispersal. In contrast, a second locus (W/w) is distributed in small patches or exhibits random spatial distribution. One explanation for the difference in average patch size is that high mutation rates coupled with strong natural selection may act to decrease the average patch size of white flowers. The mean genetic distance between populations of I. purpurea is independent of geographic distance over distances ranging from 50 m to 560 km. These data suggest moderate rates of interpopulation migration, possibly caused by agricultural activity and other forms of human-mediated dispersal.