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Lake Cress (Armoracia lacustris)

Life history

Species overview

Lake Cress (Armoracia lacustris), a Wisconsin Endangered plant, is found in still waters of lakes, rivers, estuaries. Blooming occurs early June through late August; fruiting occurs late July through late August. The optimal identification period for this species is early June through late August.

Synonyms: Armoracia aquatica, Nasturtium lacustre, Neobeckia aquatica, Radicula aquatica, Rorippa americana, Rorippa aquatica


  • Distinguishing characteristics: Distinguished from other aquatic plants with divided underwater leaves by having leaves which are also alternate and maintain a central axis.
  • Flower characteristics: Flowers white, 4-parted; petals 6 to 8 mm long, borne on spreading stalks (pedicels) 1 cm long.
  • Fruit characteristics: Oval, 5 to 8 mm long, containing one chamber, and tipped by a 2 to 4 mm long protrusion formed by the persistent style.
  • Leaf characteristics: Underwater leaves smooth and pinnately dissected into many threadlike segments; above water leaves, if present, lance shaped, 3 to 7 cm long, and sharply toothed.


  • Blooming phenology: early June through late August
  • Fruiting phenology: late July through late August
  • Optimum time to identify: The optimal identification period for this species is early June through late August


  • Growth form: Aquatic forb-submergent/emergent
  • Vegetative reproduction:
  • Life cycle: Perennial
  • Comments: Associated Species: Other aquatic macrophytes.

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

The table below provides information about the protected status - state and federal - and the rank (S and G Ranks) for Lake Cress (Armoracia lacustris). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where this species has been found to date and is not meant as a range map.

Documented locations of Armoracia lacustris in the Natural Heritage Inventory Database as of July 2015.

Summary Information
State StatusEND
Federal Status in Wisconsinnone
State RankS1
Global RankG4?
Tracked by NHIY

Habitats and landscapes

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.

General habitat information

  • Habitat description: Found in still waters of lakes, rivers, estuaries.
  • Soils: Wet soils.

Natural communities

This table lists the natural communities that are associated with Lake Cress. Scores for natural community associations are: "significant" association (score=3), "moderate association" (score=2) or the species can be present but is only weakly associated with the community (score=1).

Natural communities score
Emergent Marsh 2
Submergent Marsh 3
Floating-leaved Marsh 2

Ecological landscapes

This table lists the ecological landscape association scores for Lake Cress. The scores (3=High, 2=Moderate, 1=Low, 0=None) also correspond to the map.

Map of the Ecological Landscapes of Wisconsin.

Species guidance

The Endangered Resources Program has developed avoidance measures and management guidelines for plants on the Natural Heritage Working List. These are a work in progress, and we welcome your suggestions and feedback. Sources used in developing this information can be found here.

Avoidance measures

These are specific actions designed to avoid "take" (mortality) of this species.

  • Avoid known individual plant locations and conduct operations elsewhere when they are least likely to cause damage. Ideally, this would involve frozen, snow-covered ground. However, in areas of the state where frozen conditions are unreliable, very dry soils late in the growing season might be the best available alternative. Consult with a biologist, if needed.
  • Avoid broadcast spraying of herbicides; use care with spot spraying.

Management guidance

Management guidelines are additional considerations that may help maintain or enhance habitat for this species

  • Minimize disturbance to hydrology, including soil disturbance from rutting.
  • This species is likely sensitive to water quality. Following BMPs around streams and buffering associated drainages will reduce eutrophication and prevent water quality degradation.


Lake Cress Photo.

Photo © William S. Alverson, Wisconsin State Herbarium

Lake Cress Photo.

Photo by  staff, Wisconsin DNR.

Support for Wisconsin's rare plant information has been provided by the Division of Forestry, the Endangered Resources Fund and the Wisconsin Rare Plant Preservation Fund. To donate, visit the Natural Resources Foundation of Wisconsin [exit DNR].

Last revised: Wednesday, May 05, 2021
Southwest Savanna Southern Lake Michigan Coastal Western Coulees and Ridges Southeast Glacial Plains Central Sand Hills Central Lake Michigan Coastal Central Sand Plains Northern Lake Michigan Coastal Northern Lake Michigan Coastal Northeast Sands Western Prairie North Central Forest Northern Highlands Northwest Lowlands Northwest Sands Northwest Lowlands Superior Coastal Plains Forest Transition