High genetic diversity and low population structure in Porter’s sunflower (Helianthus porteri)

Granite outcrops in the southeastern United States are rare and isolated habitats that support edaphically controlled communities dominated by herbaceous plants. They harbor rare and endemic species that are expected to have low genetic variability and high population structure due to small populations sizes and their disjunct habitat. We test this expectation for an annual outcrop endemic, Helianthus porteri (Porter’s sunflower). Contrary to expectation, H. porteri has relatively high genetic diversity (He = 0.681) and relatively low genetic structure among the native populations (FST = 0.077) when compared to five other Helianthus species (N = 288; 18 EST-SSR markers). These findings suggest greater gene flow than expected. The potential for gene flow is supported by the analysis of transplant populations established with propagules from a common source in 1959. One population established close to a native popualtion (1.5 km) at the edge of the natural range is genetically similar to ...