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Ryan O'Connor
Natural Heritage Inventory Ecologist

Floating-leaved Marsh

State Rank: S4     Global Rank: G4G5   what are these ranks?


Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

Counties shaded blue have documented occurrences for Floating-leaved Marsh in the Wisconsin Natural Heritage Inventory database.

Floating-leaved marsh is dominated by aquatic macrophytes with leaves that rest on and cover at least 50% of the water's surface or exceed cover values for submersed and emergent macrophytes. These marshes occur on large and small lakes, especially those with irregular shorelines and protected shallow bays, shallow lakes and ponds occupying steep-sided kettle depressions, and the backwaters of large and medium-sized rivers. Water depths of about 7-8 feet favor stands of floating-leaved aquatic macrophytes and are generally greater than stands of emergent vegetation, though there can be spatial overlap.

Leaves of the floating-leaved species vary in size and shape, but in many species are round, oval, or heart shaped. Pond lilies (Nymphaea odorata, Nuphar variegata) have large leaves, and when dominant, can cover virtually the entire surface of the water in the area they occupy. Watershield (Brasenia schreberi) is also successful in doing this in many acidic, shallow marshes. Under such conditions, the heavy shading can inhibit the development of beds of submergent or emergent plants. Some macrophytes, like long-leaf pondweed (Potamogeton nodosus) and floating-leaf bur-reed (Sparganium fluctuans), have floating leaves that are narrow or strap-shaped and there is an intermediate stage in the life cycle of wild rice (Zizania spp.) when the narrow, strap-shaped leaves are flexible and float on the surface.

Floating-leaved marsh may occur with other wetland and aquatic communities (especially other marshes and sedge meadows) in poorly drained glacial landforms such as till plains and pitted outwash. It also occurs in lagoons protected by sand spits along the Great Lakes shores, especially on Lake Superior. In unglaciated southwestern Wisconsin, the community occurs mostly within the floodplains of larger rivers as well as in impoundments.

Defining Characteristics and Similar Communities

Floating-leaved marsh sometimes intergrades with emergent marsh and submergent marsh but has at least 50% cover of rooted floating-leaved aquatic plants, or is dominated by floating-leaved plants relative to submersed and emergent plants. American lotus marsh is similar to floating-leaved marsh, but is dominated by lotus, which has leaves held above the water by mid-summer, allowing more light to penetrate the water column. Wild rice marshes may resemble floating-leaved marshes early in the growing season during rice's floating-leaf stage but are classified separately.

Rare animals

Species of Greatest Conservation Need

Wisconsin Wildlife Action Plan graphic

The following Species of Greatest Conservation Need are listed according to their level of association with the Floating-leaved Marsh natural community type, based on the findings in Wisconsin's 2015 Wildlife Action Plan.

Scores: 3 = high association, 2 = moderate association, and 1 = low association. See the key to association scores for complete definitions.

Pickerel FrogLithobates palustris3

American Black DuckAnas rubripes3
Black TernChlidonias niger3
Great EgretArdea alba3
King RailRallus elegans3
Least BitternIxobrychus exilis3
Red-necked GrebePodiceps grisegena3
Yellow-headed BlackbirdXanthocephalus xanthocephalus3
American BitternBotaurus lentiginosus2
Black-crowned Night-HeronNycticorax nycticorax2
Common TernSterna hirundo2
Rufa Red KnotCalidris canutus rufa2
Whooping CraneGrus americana2
Yellow-crowned Night-HeronNyctanassa violacea2
Purple MartinProgne subis1
Short-eared OwlAsio flammeus1
Wilson's PhalaropePhalaropus tricolor1
Yellow RailCoturnicops noveboracensis1

Dragonflies and damselfliesScore
Painted SkimmerLibellula semifasciata2
Slaty SkimmerLibellula incesta2
Lilypad ForktailIschnura kellicotti1
Mottled DarnerAeshna clepsydra1
Spangled SkimmerLibellula cyanea1
Swamp DarnerEpiaeschna heros1

Grasshoppers and alliesScore
Bog ConeheadNeoconocephalus lyristes1
Spotted-winged GrasshopperOrphulella pelidna1

Big Brown BatEptesicus fuscus2
Little Brown BatMyotis lucifugus2
Northern Long-eared BatMyotis septentrionalis2
Silver-haired BatLasionycteris noctivagans1
Tricolored BatPerimyotis subflavus1

Please see Section 2. Approach and Methods of the Wildlife Action Plan to learn how this information was developed.

Rare plants

The Natural Heritage Inventory has developed scores indicating the degree to which each of Wisconsin's rare plant species is associated with a particular natural community or ecological landscape. This information is similar to that found in the Wildlife Action Plan for animals. As this is a work in progress, we welcome your suggestions and feedback.

Scores: 3 = "significantly associated," 2 = "moderately associated," and 1 = "minimally associated."
Scientific Name Common Name Score
Armoracia lacustris Lake Cress 2
Callitriche hermaphroditica Autumnal Water-starwort 1
Callitriche heterophylla Large Water-starwort 3
Caltha natans Floating Marsh Marigold 2
Nuphar advena Yellow Water Lily 3
Nuphar microphylla Small Yellow Pond Lily 3
Potamogeton bicupulatus Snail-seed Pondweed 3
Potamogeton confervoides Algae-leaved Pondweed 1
Potamogeton diversifolius Water-thread Pondweed 3
Potamogeton oakesianus Oakes' Pondweed 3
Potamogeton pulcher Spotted Pondweed 3
Potamogeton vaseyi Vasey's Pondweed 3
Schoenoplectus torreyi Torrey's Bulrush 2


The following Ecological Landscapes have the best opportunities to manage for Floating-leaved Marsh, based on the Ecological Landscapes of Wisconsin Handbook.

Map of the Ecological Landscapes of Wisconsin.

Major (3 on map)
A major opportunity for sustaining the natural community in the Ecological Landscape exists, either because many significant occurrences of the natural community have been recorded in the landscape or major restoration activities are likely to be successful maintaining the community's composition, structure, and ecological function over a longer period of time.

Important (2 on map)
Although the natural community does not occur extensively or commonly in the Ecological Landscape, one to several occurrences do occur and are important in sustaining the community in the state. In some cases, important opportunities may exist because the natural community may be restricted to just one or a few Ecological Landscapes within the state and there may be a lack of opportunities elsewhere.

Present (1 on map)
The natural community occurs in the Ecological Landscape, but better management opportunities appear to exist in other parts of the state.


Wisconsin Wildlife Action Plan graphic

What are conservation actions?

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for natural communities


Floating-leaved Marsh Photos

Floating-leaved Marsh Photo

Example of some of the overlap that occurs in marshes with varying water depths. Beds of white water-lily interspersed with protruding spears of very tall wild rice stems.

Photo by Eric Epstein.

Floating-leaved Marsh Photo

Floating leaf marsh with Brasenia sp. in Jefferson Co.

Photo by Brenton Butterfield.

Floating-leaved Marsh Photo

Floating leaved marsh containing Nuphur variegata (bull-head pond-lily) in Jefferson Co.

Photo by Brenton Butterfield.

Floating-leaved Marsh Photo

Floating leaved marsh containing Nymphaea ordata (American white water lily, fragrant water-lily) in Vilas Co.

Photo by Brenton Butterfield.

Floating-leaved Marsh Photo

Floating leaved marsh containing Sparganium fluctuans (floating-leaved bur-reed) in Oneida Co.

Photo by Brenton Butterfield.

Note: photos are provided to illustrate various examples of natural community types. A single photograph cannot represent the range of variability inherent in a given community type. Some of these photos explicitly illustrate unusual and distinctive community variants. The community photo galleries are a work in progress that we will expand and improve in the future.

Last revised: Tuesday, August 30, 2022