Champlain beachgrass (Ammophila champlainensis) was described by Seymour in 1966 as endemic to the shores of Lake Champlain in Vermont and New York. Some later authors have recognized it while others have not, or they have treated it at a different rank. In order to resolve the issue of the recognition and appropriate rank, nine characters, including those suggested by previous authors as important to distinguish this taxon, were measured in 457 specimens from throughout the northeastern North American range of Ammophila. A reduced data set of 281 specimens and seven characters was studied using: (1) analysis of variance to determine optimal characters for differentiating geographical groups; (2) scatter plot analysis of optimal characters; (3) principal component analysis to investigate the major trends in pattern of variation without character weighting; (4) discriminant analysis to determine the extent of differentiation using a weighted formula; and (5) linear regression to reveal trends in variation related to size of associated water bodies. The analyses failed to clearly separate the plants from Lake Champlain from other Ammophila populations. However, the Lake Champlain plants were the most discrete of nine natural geographic groups, followed by plants from Lac Saint-Jean, and then plants from the Atlantic coast. None of the geographic groups was sufficiently different to justify recognition of distinct taxa due to the extensive overlap in measurements of characters. Populations adjacent to smaller water bodies, where dunes tend to be smaller and less active, tend to have smaller plants with smaller parts. Plants from Lake Champlain, including those described and identified as A. champlainensis, and all other northeastern populations of Ammophila, are best treated as the single species A. breviligulata.