2017 ASHS Annual Conference

Helianthus verticillatus, the whorled sunflower, is an endangered species endemic to only a few locations in Tennessee, Alabama, and Georgia. This sunflower is an aggressive grower and attractive to both plant enthusiasts and pollinators with its multiple, small yellow flowers in late fall. There is no conservation plan for this species because of large gaps in knowledge in the plant’s basic biology, and fine-scale population structure, and little census data is available. The objectives of this study were to better understand the fine-scale genetic diversity and the spatial population structure of H. verticillatus. Two small sites in Georgia separated by less than a kilometer of densely forested land were sampled. Fourteen published microsatellite loci from H. verticillatus were used to assess genetic diversity and population structure of the plants in the sampling areas. Our results indicated moderate genetic diversity, limited gene flow and high genetic differentiation among H. verticillatus subpopulations. Two distinct genetic clusters, one located on either side of the forested barrier, were detected, and furthermore, little gene flow was evident between the two groups. We found significant heterozygosity excess, indicating presence of population bottleneck due to recent reduction in population size. The standardized index of association, a measure of linkage disequilibrium, was significantly different from zero, supporting the hypothesis of extensive and significant clonal reproduction among H. verticillatus subpopulations. Overall, these results have major implications for the population fitness, and survival of this species, and points to the immediate need to develop and implement a recovery plan for H. verticillatus.