To determine the extent to which natural populations vary in levels of developmental instability, meristic variation was assessed in fourteen wild populations of Phlox drummondii growing in central Texas. There were significant differences among populations in the percentages of flowers that exhibited an abnormal number of sepals and anthers, but not petals or stigmatic lobes. Of the four whorls, stigmatic lobes varied the most with 4.5% of the flowers exhibiting an abnormal number. Overall, 8.2% of the 5,022 flowers scored had at least one anomalous flower. In a separate greenhouse study, five cultivars and three natural populations of P. drummondii were grown simultaneously to determine the extent to which the domestication process has influenced meristic variability. Cultivars exhibited significantly greater floral formula variation in all four whorls compared to their wild progenitors. As with the survey of wild populations, stigmatic lobes varied the most with 17% of the flowers exhibiting an abnormal number of lobes in the cultivated populations.

Key words: Developmental Instability, Floral Formula, Meristic Variation, Phlox