A parsimony algorithm was used to evaluate the distribution and co-occurrence of 46 vascular salt marsh-associated species in 20 coastal salt marshes from Biscayne Bay National Park, FL, to Sable Island Marine Protected Sanctuary, NS, Canada. The method considers each salt marsh as if it were a taxon, and the presence or absence of a particular vascular plant species as a “character state” of that taxon. Using this information, a 20 × 46 data matrix was created and examined by multivariate ordination techniques and by parsimony analysis using the program WinClada running over NONA. A hierarchical clustering showed that the salt marsh sites on the eastern seaboard of North America formed two main clusters, one including all of the Florida sites and South Carolina, and the second including all of the more northern sites: North Carolina, Virginia, New Jersey, New York, and Sable Island, NS, Canada. Within the large southern cluster, we find two major sub-clusters separating the Florida marshes from those of South Carolina. Likewise, within the large northern cluster, we find two major sub-clusters separating North Carolina and Virginia from the other northern marshes. An essentially similar pattern of site grouping was also observed using the ordination technique of non-metric multidimensional scaling, in which the southern marshes all aligned to the left of the origin, while the more northern marshes align to its right. Parsimony analysis yielded twelve equally parsimonious trees from which a strict consensus tree was constructed. The topology of the consensus tree clearly shows two major clades, a southern one and a northern one, with the division occurring between South and North Carolina. The main southern clade is supported by the presence of Sporobolus virginicus (Seashore Dropseed), while the main northern clade is supported by the presence of Ruppia maritima (Widgeongrass). Spartina alterniflora (Smooth or Atlantic Cordgrass), which we take as the single species that defines the salt marsh on the eastern coast of North America, was present in all of the sampled sites except Biscayne Bay National Park, FL, a mangrove swamp.