The discovery of three populations of the large-headed sedge, Carex macrocephala, in New Jersey described in this paper, represents the first report of this species from Eastern North America. Carex macrocephala grows at much lower densities in New Jersey than does the closely related Asiatic sand sedge, Carex kobomugi. We thus expected invasion by C. macrocephala to have less impact of on the abundance and diversity of native dune plants than have been seen in previous studies of the closely related invasive sedge, C. kobomugi. This expectation was largely supported: the presence of C. macrocephala in New Jersey's coastal dunes had no significant impact on the abundance of co-occurring plant species. Indeed, species richness and diversity were actually significantly higher in areas occupied by C. macrocephala than in surrounding areas. New Jersey appears to be one of the few places in the world where C. macrocephala grows in close proximity to C. kobomugi, suggesting the possibility of hybridization between these species in the future. Since hybrids have the potential to be more invasive than their parent species, this has serious management repercussions.