Environmental Description:  This association occurs in two distinct environments. Along freshwater to slightly oligohaline stretches of tidal rivers and large tidal tributaries, it forms narrow (typically 5- to 10-m) bands in the low intertidal zone adjacent to channel margins. This community also occupies small (generally <0.3 ha) depressions or open mudflats near the mouths of tidal guts or in the interior of marshes, where subsidence has locally lowered the level of the substrate and consequently increased the duration of inundation from diurnal lunar tides. If they are not proximate to an interior channel, such subsidence zones may not drain completely during every tidal cycle, thus resulting in a different salinity regime than the surrounding higher marsh. In prevailing fresh to slightly oligohaline conditions, these patches may concentrate salt, but more typically, lenses of less saline water may persist under a strongly oligohaline to mesohaline regime. Under both sets of environmental conditions, the substrate consists of mucky clay or fine-textured silt, often with abundant organic matter.