In each of the three edaphic endemic varieties of Phacelia dubia, populations have been observed in weedy roadsides and lawns. Plants in the weedy populations differ ecologically and morphologically from plants in populations historically restricted to granite outcrops or cedar glades. The weedy populations tend to occur in full sun at very high densities, their plants mature at a small size, and they flower approximately one month before nearby outcrop/glade populations. Common garden experiments using plants derived from seeds of P. dubia var. georgiana collected from a weedy site and a nearby granite outcrop showed no size differences between populations when grown under either high light or partial shade conditions. In the shade treatment, plants from both populations failed to flower for the duration of the experiment, but in the sun treatment, significantly more plants derived from the weedy population flowered, and for those plants that flowered, bud production was much higher in plants from the weedy population. A search of herbarium records showed that for each variety, weedy occurrences first appeared between 1972 and 1984. The experimental data showed the weedy phenotype has arisen through a combination of phenotypic plasticity and genetic change, whereas the herbarium record suggests that evolution of the weedy ecotypes is a recent event that has arisen independently in each variety.