Physiognomy and Structure: These are graminoid herb dominated wetlands.

Floristics: This alliance includes wetlands dominated or codominated by Fimbristylis castanea or Schoenoplectus pungens that often occur in interdune swales on the southeastern coast, from Delaware to Florida. This alliance is documented from Assateague Island National Seashore (Higgins et al. 1971, Hill 1986), where it is typically characterized by dense Schoenoplectus pungens (= Scirpus pungens) (up to 80% cover). When Schoenoplectus pungens is not as dense, it is most often associated with an even mixture of Spartina patens or Fimbristylis castanea. In spring, Schoenoplectus pungens is generally dominant with few other associates except Eleocharis spp., imparting a distinct aerial photo-signature. By late summer a number of other species, such as Fimbristylis castanea and Sabatia stellaris, contribute more substantial cover. Other herbs are sparse and contribute very little to the overall vegetative cover. These associated species include Andropogon virginicus, Eleocharis parvula, Eleocharis rostellata, Fimbristylis autumnalis, Hydrocotyle umbellata, Juncus canadensis, Juncus scirpoides, Panicum amarum var. amarulum, Phragmites australis, Pluchea foetida, Ptilimnium capillaceum, and Sabatia stellaris. Diagnostic species are Eleocharis spp., Fimbristylis castanea, Juncus spp. and Schoenoplectus pungens. There is usually standing water present in these swales in the spring. In Florida, these are early-successional, interdunal swales which are dominated by Fimbristylis castanea, sometimes monospecific, sometimes intermixed with Triglochin striata, Sesuvium portulacastrum, and Lilaeopsis carolinensis.

Dynamics:  This vegetation occurs in southern coastal interdunal swales. These sites are not subject to regular tides, but may be exposed to saltwater from storm surges and seasonal high tides. High wind and storm surges can alter the position of dunes and swales. These are dynamic landforms which change as part of natural coastal processes.