Environmental Description:  Stands occur in intertidal and subtidal areas of estuaries along the ocean coasts or in semipermanently to permanently flooded areas of inland saline marshes and creeks (these inland areas are primarily in arid areas of western North America). The minimal depth limits of the beds are determined by low or high tide levels and the maximum depth limits by the penetration of light sufficient for photosynthesis, the latter being a function of water depth and water clarity. Kanrud (1991) identified maximum depth at 4 m. Beds generally occur in areas with moderate current velocities (<-50 cm/sec in Chesapeake Bay (Koch et al. 2000)) and, usually, moderate wave action. Koch et al. (2000) noted that the "canopy-forming" Zannichellia palustris was more limited by wave action than the "meadow-forming" Stuckenia pectinata (Ruppia maritima is a meadow-forming species, but its flowering/fruiting structures are wave sensitive). Water salinity in coastal areas ranges from oligohaline to mesohaline. In the Chesapeake Bay of Maryland and Virginia, stands that can be assigned to this division (Ruppia and Potamogeton Communities of Moore et al. (2000)) occupy areas that experience average spring salinities of 1-11 practical salinity units (psu) and average autumn salinities of 6-18 psu (Schubel and Pritchard 1987, Moore et al. 2000). Water chemistry in inland stands and in isolated lagoons and pools may be hypersaline (Ito et al. 2010).

Climate: Climate spans a wide range, from subtropical to sub-boreal and from humid to arid. Stands are found from slightly below sea level along the coasts to at least 2800 m (9100 feet) in Colorado.

Soils/substrate: Substrates are muddy to sandy. Through literature review, Koch et al. (2000) concluded that mixtures of Ruppia maritima, Vallisneria americana, Stuckenia pectinata, and Potamogeton perfoliatus persisted on substrates consisting of from 5-90% fine materials (<63 mm) and that the latter two species could be found on silty substrates. Overly fine substrates as less likely to support healthy beds because of decreased pore water exchange with the overlying water column and greater potential for sulfide accumulations; overly coarse sediments have lower nutrient content (Koch et al. 2000). Generally, substrates have less than 5% organic matter content (Koch et al. 2000).

Biogeography: This vegetation is found throughout most biotic regions of temperate North America. The vascular plant floristic composition is relatively uniform throughout and, within its geographic range, its occurrence appears to be more a result of water chemistry conditions than of climate.