Northern Prairie Wildlife Research Center
Wetland Plants and Plant Communities of Minnesota and Wisconsin
The primary purpose of this guide is to assist U.S. Army Corps of Engineers
(Corps) personnel working with the regulatory program under Section 404 of the
Clean Water Act and Section 10 of the Rivers and Harbors Act of 1899. It provides
an easy-to-use, pictorial guide to wetlands primarily for individuals who are
not botanists, although botanists may also find it useful. A secondary purpose
is to provide a guide for individuals working with other agencies and programs
dealing with wetlands. Finally, this guide serves to enhance public awareness
of wetlands by illustrating their diversity and values.
The guide specifically addresses wetland plants and plant communities of Minnesota
and Wisconsin (Figures 1 and 2), but is applicable
in general to wetlands of the entire Great Lakes Region. Note that the 144 plant
species included in the guide do not represent, nor are they intended to represent,
a listing of all plant species found in wetlands of Minnesota and Wisconsin.
For a complete listing of these species, refer to the botanical references listed
in the bibliography.
This guide is organized by wetland plant community. In general, the wetland
plant communities are organized according to water permanence and depth, and
degree of soil saturation. Thus, the guide progresses from deepwater wetlands
(I. Shallow, Open Water Communities) to temporary water-holding wetlands (VIII.
Seasonally Flooded Basins). Photographs and descriptions are provided for each
of the fifteen wetland plant communities, along with representative plant species
of each. A particular plant species may occur not only in the wetland plant
community under which it is listed, but in other wetland communities, and in
some cases, upland communities. The other communities in which an individual
plant species may frequently occur are provided under ECOLOGICAL NOTES.
Note that upland plants occasionally occur in wetlands and, conversely, wetland
plants occasionally occur in upland habitats. This is especially true in transitional
areas between wetlands and uplands.
The definition of wetlands used by the Corps in its regulatory program is:
Wetlands are those areas inundated or saturated by surface or groundwater
at a frequency and duration sufficient to support, and that under normal circumstances
do support, a prevalence of vegetation typically adapted for life in saturated
soil conditions. Wetlands generally include swamps, marshes, bogs, and similar
areas (33 CFR 328).
Refer to the Corps of Engineers Wetlands Delineation Manual (Environmental
Laboratory 1987), or current federal manual, for a Methodology to apply this
definition in the field.
CONCEPT OF A HYDROPHYTE
Wetland plants are hydrophytes (hydro = water, phyte = plant). These
are plants growing in water or on a substrate that at least periodically is
deficient in oxygen due to excessive water content. Hydrophytes have morphological,
physiological and reproductive adaptations that allow them to thrive in inundated
or saturated soils where non-hydrophytes (upland plants) cannot. Communities
dominated by hydrophytes are referred to as hydrophytic plant communities.
CLASSIFICATION OF WETLANDS
A number of wetland classification schemes have been developed. Table
1 compares the fifteen plant communities of this guide to classification
systems developed by Shaw and Fredine (1971), Cowardin et al. (1979),
Curtis (1971), and the Wisconsin Wetland Inventory. As shown in Table 1, the
fifteen plant communities of this guide correspond most closely to the wetland
plant communities described by Curtis (1971) in The Vegetation of Wisconsin.
VEGETATION TENSION ZONE
Throughout the guide are references to a vegetation tension zone. The flora
of Minnesota and Wisconsin is arranged in two major floristic provinces. A floristic
province is a large area with a relatively uniform flora, delineated by a tension
zone in which many species reach a common range boundary (Curtis 1971).
The vegetation tension zone then is a band between two floristic provinces
marked by the intermingling of species from both (Curtis 1971). The two floristic
provinces in Minnesota and Wisconsin are the "northern forest floristic province"
and the "prairie- forest floristic province," which are illustrated by Figure
3. The vegetation tension zone through Wisconsin is shown according to Curtis
(1971). A tentative vegetation tension zone through Minnesota is extrapolated
from the original vegetation map of Minnesota compiled by Marschner (1930).
A portion of the "prairie-forest floristic province" in southern and western
Minnesota deserves special mention. It is part of the Prairie Pothole Region
(Figure 4). Prairie potholes are shallow, water-holding depressions of glacial
origin found in the prairies of north-central United States and south-central
Canada (Sloan 1972). These wetlands have great variability in size, depth, water
permanence, and water chemistry (Sloan 1972, Stewart and Kantrud 1972). For
example, prairie potholes can range in size from less than one quarter acre
to several thousand acres. In terms of water permanence and depth, prairie potholes
range from seasonally flooded basins that hold water for only a few weeks each
year, to wet prairies, to shallow and deep marshes, to permanent open water.
Water chemistry can be fresh, mixosaline, saline, or hypersaline. Multiple year
wet and drought cycles are typical in the Prairie Pothole Region.
|Figure 3 (The Wisconsin portion of this figure is adapted from
an illustration copyrighted by the University of Wisconsin Press. It
is used here by permission.)
|Figure 4 - Generalized Original Limits of the Prairie Pothole
Region of the U.S. and Prairie Provinces of Canada (adapted from Sanders
Prairie potholes are extremely important for North American waterfowl production.
Although prairie potholes comprise only 10 percent of potential waterfowl
breeding habitat in North America, it is estimated that 50 percent of waterfowl
production occurs in these wetlands, with an even higher percentage occurring
in wet years (Sloan 1972). Agricultural practices continue to degrade or destroy
these important wetlands. However, there are federal, state and private programs
and participants working to restore prairie potholes and the important functions
and values they provide.
| The above photograph shows a deep marsh prairie pothole dominated
by river bulrush (Scirpus fluviatilis) and hardstem bulrush (Scirpus
acutus). It is part of the Victory Wildlife Management Area in Big
Stone County, Minnesota.
North of the vegetation tension zone is another group of wetlands deserving
special mention. These are the patterned peatlands of northern Minnesota. A
notable example is the Red Lake Peatland, which covers nearly 500 square miles,
making it one of the largest continuous tracts of peatlands in the conterminous
United States (Glaser et al. 1981). "Patterned" refers to the distinct
and frequently striking landforms that compose these peatlands. Flarks, strings,
ovoid islands, teardrop islands, raised bogs and fens are examples of names
applied to these patterned landforms. Some of the plant associations of the
patterned peatlands correspond to the communities described herein. However,
other associations of patterned peatlands are not specifically described. Discussion
of these specialized plant associations goes beyond the scope of this generalized
guide. For a detailed description of the patterned peatland communities, publications
such as Glaser et al. (1981) and Wright et al. (1992) should be
Below is a color infrared aerial photograph showing a portion of the Red
Lake Peatlands in Beltrami County, Minnesota. Visible peat landforms and vegetation
patterns include the following (numbers correspond to those on the photograph):
- Water tract where runoff is channeled across the peat surface; includes
strings (peat ridges) and flarks (pools) arranged perpendicular to the direction
of water flow. Dominant vegetation includes sedges (Carex).
- Streamlined tree islands (mostly tamarack with some black spruce) tapered
in the direction of water movement.
- A smaller internal water tract.
- Sphagnum lawn.
- Ovoid island with a horseshoe-shaped black spruce forest and a non-forested
- Straight lines are drainage ditches, the result of a failed attempt to
drain the peatlands during 1905-1929.
Interpretation of aerial photography is from Wright et al. (1992).
The area shown by the photograph covers approximately 16 square miles.
| Red Lake Peatlands
Millions of acres of wetlands in Minnesota and Wisconsin have been effectively
drained and converted to non-wetland during the past 150 years, primarily for
purposes of agricultural use. Millions of additional acres of existing wetlands
are: (1) partially drained and cropped; or, (2) cropped under natural conditions
(e.g., during dry periods). Partially drained refers to cases where wetland
hydrology has been altered by such measures as ditching and/or tiling, but the
area still retains sufficient hydrology to meet wetland criteria [e.g., see
the Corps of Engineers Wetlands Delineation Manual (Environmental Laboratory
1987)]. An example is a deep marsh plant community that is ditched and converted
to a fresh (wet) meadow community.
The example of a farmed wetland shown by the photograph is a shallow marsh
prairie pothole basin that had been plowed and planted to corn, an upland
species, at the start of the growing season. By midsummer, ponding and saturated
soil conditions had resulted in drown out and crop stress (yellowed, stunted
corn). The dark green vegetation in the basin is softstem bulrush (Scirpus
validus), an obligate wetland plant, which is recolonizing the basin in
spite of plowing earlier in the growing season.
NATIONAL WETLAND PLANT LIST
As part of the National Wetland Inventory undertaken by the U.S. Fish and Wildlife
Service (Service), a wetland plant list has been developed by the Service in
cooperation with a federal interagency review panel (Reed 1988, 1996). This
list ranks individual plant species according to their probability of occurrence
in wetlands as shown below.
- Obligate Wetland (OBL). Almost always occurs in wetlands (estimated
probability > 99%) under natural conditions.
- Facultative Wetland (FACW). Usually occur in wetlands (estimated
probability 67%-99%), but occasionally found in non-wetlands.
- Facultative (FAC). Equally likely to occur in wetlands (estimated
probability 34%- 66%) or non-wetlands.
- Facultative Upland (FACU). Usually occur in non-wetlands (estimated
probability 67%-99%), but occasionally found in wetlands (estimated probability
- Obligate Upland (UPL). Occur almost always (estimated probability
> 99%) in non-wetlands under natural conditions.
A positive (+) and negative (-) sign is used for the facultative categories.
The (+) sign indicates a frequency towards the wetter end of the category
(more frequently found in wetlands) and the (-) sign indicates a frequency
towards the drier end of the category (less frequently found in wetlands).
A wetland indicator status that is in brackets [ ] reflects the opinion
of the authors as to the probability of occurrence in wetlands of that particular
At the time this field guide went to press, the 1996 National List of
Plant Species That Occur In Wetlands (Reed 1996) was in draft form for
public review and comment. Since it was unknown what proposed changes would
be adopted by the final version, the authors of this field guide primarily
used the indicator status given by Reed (1988).
FACU DOMINATED WETLANDS
FACU species occur in wetlands 1 to 33 percent of the time and, in some cases,
can be dominant species in wetlands. Examples include white pine (Pinus strobus)
or jack pine (Pinus banksiana) swamps. The photograph shows a swamp dominated
by white pine in Monroe County, Wisconsin. Soils are Dawson peat, a very poorly-
drained organic soil. Hydrology is primarily groundwater seepages. No hydrologic
modifications (e.g., ditching, tiling) have occurred at this site. Other plant
species present are OBL or FACW species such as speckled alder (Alnus incana
ssp. rugosa), skunk cabbage (Symplocarpus foetidus) and cinnamon
fern (0smunda cinnamomea). Mature white pines have formed raised hummocks
caused by shallow rooting, apparently a response to saturated soil conditions.
Another case where FACU species may dominate are seasonally flooded basins
that are ponded early in the growing season, but are dry for much of the remainder
of the growing season. See discussion of seasonally flooded
basins. In addition, FACU species may dominate wetland basins during periods
of drought, such as the multiple year drought cycles experienced in the Prairie
Nomenclature follows Gleason and Cronquist (1991). However, a few exceptions
were made in response to recent changes of nomenclature for certain species
(e.g., Kartesz 1994). Common names were selected at the discretion of the authors.
Occasionally, the following format is used for listing measurements of a given
character: (2)3-5(6) mm. This means the character is typically 3 to 5 mm. in
size, but can range from a minimum of 2 mm. to a maximum of 6 mm.
The following abbreviations are used in the text.
- mm. -- millimeter(s)
- cm. -- centimeter(s)
- dm. -- decimeter(s)
- m. -- meter(s)
- sp. and spp. -- species (singular) and species (plural)
- ssp. -- subspecies
- var. -- variety
- dbh -- diameter at breast height
Photographs are by Steve D. Eggers except for the following:
Donald M. Reed - Lake sedge closeup; swamp aster growth form.
Welby R. Smith - Western prairie fringed orchid.
Minnesota Department of Natural Resources - Aerial photography of the Red
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