Vegetation patterns in the coastal salt pond marsh system at Odiorne Point State Park in Rye, New Hampshire, the state's only viable example, are described based on recent surveys and historical data. Four natural communities occur within the system: coastal salt pond flat, coastal salt pond emergent marsh, coastal salt pond meadow marsh, and highbush blueberry–winterberry shrub thicket. The first three communities are newly described in New Hampshire and the northeastern US coastline. A total of 69 native or naturalized vascular plant taxa from 54 genera and 33 families have been documented in the system at Odiorne Point between 1967 and 2011. The families best represented were Cyperaceae (10 taxa), Poaceae (9 taxa), and Asteraceae (6 taxa); the largest genera were Eleocharis (4 taxa), Hypericum (4 taxa), and Agrostis (3 taxa). In 2011, only 35 of the 69 plant taxa were documented; a difference that can be attributed, at least partially, to the variable nature of hydrologic and salinity influences on the system. Of the 69 plant taxa, three are rare in New Hampshire and five are both non-native and invasive in the state and region. The uncertainty of the nativity status of Typha angustifolia, the dominant species in the marsh, has significant implications for future management decisions. Measurement of surface and pore water salinity in late summer of 2011 revealed essentially fresh water conditions at the surface (1.1 ± 0.5 ppt SE), whereas pore water occurring 10 cm and 40 cm below the soil surface was mesohaline (5.8 ± 1.8 and 8.1 ± 1.8 ppt SE, respectively). Mean pore water salinity differed significantly among the natural communities examined, suggesting that hydrology and salinity influence species composition and distribution within coastal salt pond marsh systems. This globally rare system, distributed from Maine to New Jersey, shares similar dominant species across its range, although some of the state rare species it supports differ along a latitudinal gradient.