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Scarlet Loosestrife (Ammannia robusta)

Life history

Species overview

Scarlet Loosestrife (Ammannia robusta), a Wisconsin Special Concern plant, is found near edges of ponds, in grassy swales, and similar wet places. Blooming occurs July through September; fruiting occurs mid-August through mid-October. The optimal identification period for this species is mid-August through early October.

Synonyms: None


  • Distinguishing characteristics: Can be distinguished from Rotala sp., by its larger and showier fruits as well as its arrangement of flowers, which are clustered in the axils in Ammannia but solitary in Rotala.
  • Flower characteristics: Small, pale lavender, 1 to 3, borne in leaf axils.
  • Fruit characteristics: Capsule occassionaly dehiscent, globose.
  • Leaf characteristics: Opposite, thick and fleshy, linear or narrowly oblong, clasping to perfoliate, up to 10 cm long and 1.5 cm wide.


  • Blooming phenology: July through September
  • Fruiting phenology: mid-August through mid-October
  • Optimum time to identify: The optimal identification period for this species is mid-August through early October


  • Growth form: Forb-erect
  • Vegetative reproduction:
  • Life cycle: Annual
  • Comments: Associated Species: Echinochloa crus-galli, Scirpus sp., Juncus sp., Cyperus esculentus, Eleocharis spp, Bidens spp.

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 Scarlet Loosestrife (Ammannia robusta). 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 Ammannia robusta in the Natural Heritage Inventory Database as of July 2015.

Summary Information
State StatusSC
Federal Status in Wisconsinnone
State RankS2
Global RankG5
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 near edges of ponds, in grassy swales, and similar wet places.
  • Soils: Wet soils.

Natural communities

This table lists the natural communities that are associated with Scarlet Loosestrife. 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
Southern Sedge Meadow 3

Ecological landscapes

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

Map of the Ecological Landscapes of Wisconsin.

Ecological landscape score
Central Sand Hills 2
Southeast Glacial Plains 2

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

  • Prescribed burns and/or brushing may be beneficial (dependent on local site conditions).
  • Maintain and restore open habitat through selective clearing and brushing.
  • Minimize disturbance to hydrology, including soil disturbance from rutting.


Scarlet Loosestrife Photo.

Photo © Emmet Judziewicz.

Scarlet Loosestrife Photo.

Photo © Emmet Judziewicz.

Scarlet Loosestrife Photo.

Photo © Emmet Judziewicz.

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, October 14, 2020
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