“Pimple” dunes are small, rounded coastal dunes that form along major dune ridges of the barrier islands along the Eastern Shore of Virginia. Although most pimple dunes are small structures ranging between 10 and 20 m in diameter, they have distinct plant assemblages that replicate the upland ecotones of their barrier islands. We examined the relationship between microenvironment, edaphic factors, and plant assemblage structure on pimple dunes. Water availability was an obvious major ecological driver, but we also tested other environmental factors that may correlate with plant assemblage structure. We found distinct assemblage types that segregated themselves by habitat type: marsh, shrub thicket, and dry summit. Freshwater availability was important in delineating vegetation differences, both among transects and among species. However, soil nutrients, such as ammonium, potassium, magnesium, and boron, were also spatially correlated with plant assemblage structure. We hypothesize that interactions between water and other environmental factors (e.g., the accumulation of nutrients in the marsh after they are leached from the dune summits) are important determinants of plant species distribution and abundance, and suggest that more attention be given to micronutrients in future phytosociological studies of barrier islands.