PROTECTING WISCONSIN'S BIODIVERSITY

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Scientific Name	Common Name	Global Rank	State Rank	Federal Status	WI Status

Lake Cress (Armoracia lacustris)

State Status: END

Federal Status: none

State Rank: S1

Global Rank: G4?

Photo by WDNR Staff

Counties with Mapped NHI Occurrences

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 late-July through late-August. The optimal identification period for this species is early-June through August.

Synonyms:

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

Identification

Lake cress is a submergent/emergent aquatic forb with a smooth stem and 4-parted white flowers with 6-8mm petals borne on spreading stalks 1cm long. Its fruit are oval, 5-8mm long, contain one chamber, and are tipped by a 2-4mm long protrusion formed by the persistent style. The underwater leaves are smooth and pinnately dissected into many threadlike segments. The above water leaves, if present, are lance shaped, 3-7cm long, and sharply toothed.

Distinguishing Characteristics and Similar Species

It is distinguished from other aquatic plants with divided underwater leaves by having leaves that are also alternate and maintain a central axis.

Phenology and Reproduction

Phenology

Blooming occurs early-June through late-August, fruiting late-July through late-August.

Life Cycle, Optimum Time to Identify

Perennial. The optimal identification period for this species is early-June through August.

Ecology and Associated Species

Associated species include other aquatic macrophytes.

Habitat

Lake cress is found in still waters of lakes, rivers, and estuaries.

Avoidance Measures and Management Guidance

Avoidance Measures

Avoid broadcast spraying of herbicides and use care with spot spraying.

Management Guidance

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.

Wildlife Action Plan

Associated Natural Communities and Ecological Landscapes

Species of Greatest Conservation Need (SGCN) are associated with habitats (or natural communities) and places on the landscape. Understanding relationships among SGCN, natural communities and ecological landscapes help us make decisions about issues affecting SGCN and their habitat and how to respond. Download the Wildlife Action Plan association score spreadsheet to explore rare species, natural communities and ecological landscape associations

Issues/Threats and 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 Wisconsin Wildlife Action Plan because lack of information can threaten our ability to successfully preserve and care for natural resources.

PROTECTING WISCONSIN'S BIODIVERSITY

Lake Cress (Armoracia lacustris)

Rare Species & Natural Communities

Additional Resources

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