The plant community of a coastal beach typically shows great spatial heterogeneity in distribution and abundance. Solidago sempervirens (seaside goldenrod) is a large perennial that can potentially impact the many smaller annual plants, both native and exotic, that comprise the primary vegetation in the pioneer zone. The primary question addressed was: do plants of two native and two alien annuals nearer to S. sempervirens show a detectable reduction in density and size compared to those further away? Populations of Triplasis purpurea and Cenchrus tribuloides (native grasses), and Digitaria sanguinalis and Mollugo verticillata (ruderals), were surveyed in quadrats at distances of 20–200 cm from S. sempervirens individuals at Miller Field Beach, Staten Island, NY. Densities of both native grasses and D. sanguinalis, but not M. verticillata, showed significant reductions closest to S. sempervirens. Size of C. tribuloides was significantly reduced close to S. sempervirens. Intraspecific density had an effect on T. purpurea size, but not proximity to S. sempervirens. Because the opportunistic weeds were not greatly affected by S. sempervirens, it is suggested that the effect of seaside goldenrod on this beach community, whatever the mechanism, is primarily manifested by a reduction in the density of the native species T. purpurea and C. tribuloides. Seaside goldenrod joins American beachgrass (Ammophila breviligulata) as another perennial apparently structuring annual coastal plant communities.