Coastal Plain marsh is limited to a few sites within the sandy beds or margins of extinct glacial lakes, on level or gently sloping glacial outwash sands, and, possibly, in glacial tunnel channels. Layers of fine-textured, relatively impermeable materials occur at shallow depths beneath the surface of at least some of these waterbodies and wetlands, and they're probably essential to normal hydrologic function. The lake or pond waters are nutrient-poor and acidic, and all known occurrences of the community are small, or at most, medium-sized. Historically the surrounding vegetation included oak and pine barrens, dry acid forests composed of oaks, pines, or mixtures, sand prairie, and various peatland communities. Periodic wildfire would have been the major disturbance force in all of these communities prior to European settlement and the implementation of fire suppression policies.
Coastal plain marsh develops on sandy lake or pond shores, sometimes with the sandy waterbody margins partially covered by localized, discontinuous layers of shallow peat or muck. At several sites in central Wisconsin, members of the coastal plain marsh community - including some of the rare disjuncts - have colonized, at least temporarily, ditches, borrow pits, log landings, and haul roads. At all of these sites, the ranker, overlying vegetation has been stripped away, exposing wet sand that may be fed by slow groundwater seepage from the surrounding uplands. Sometimes in these sites there are shallow excavations, creating small ponds. The long-term conservation values of such sites are uncertain, as is the source of propagules for the flora that colonizes them. In the natural systems, many, if not most of the propagules come from the local seedbank. In those sites that are of anthropogenic origin, the source is unclear, but it seems likely that, for some species, dispersal may be aided by animals (especially, but perhaps not limited to, migratory birds), and by water moving through the ditches.
The vegetation often demonstrates strong zonation, with water depth the determinant factor. The deeper, more permanent waters support aquatic macrophytes such as water-shield (Brasenia spp.), pondweeds (Potamogeton spp.), and bladderworts (Utricularia spp.). The inshore shallows and pond margins are often dominated by diverse assemblages of short or medium stature graminoid plants including grasses, sedges (e.g., from the genera Cyperus, Eleocharis, Fimbristylis, Fuirena, Rhynchospora, Scleria, and Scirpus), and rushes (Juncus spp.), as well as forbs like milkworts (Polygala cruciata and P. sanguinea), tooth-cup (Rotala ramosior), meadow-beauty (Rhexia virginica), lance- leaved violet (Viola lanceolata), yellow-eyed grass (Xyris tora), and several of the small St. John's-worts (Hypericum spp.). The uppermost, seldom-inundated margins of the wetland are typically vegetated with more robust perennials, such as grass-leaved goldenrod (Euthamia graminifolia), Canada bluejoint grass (Calamagrostis canadensis), hardhack (Spiraea tomentosa), meadowsweet (Spiraea alba), boneset (Eupatorium perfoliatum), spotted Joe-Pye-weed (Eutrochium maculatum), and asters.
Coastal plain marsh was not recognized as a distinct community by Curtis (1959), though he did acknowledge the presence of a coastal plain flora in the state. The unusual distributions of the coastal plain plants have long been recognized by Wisconsin botanists, however. Most of the information on this type comes from farther east; Michigan, Indiana, Ontario, and New York. In Michigan and Indiana, the distribution of this community is strongly correlated with post-glacial levels of Lake Michigan. Wisconsin occurrences support fewer of the rarities and extreme disjunct species than stands in Michigan and points eastward, but the same general patterns of geographic origin and distribution, and many habitat similarities, are in evidence.
