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Flat-stemmed Spike-rush (Eleocharis compressa var. compressa)

Life history

Species overview

Flat-stemmed Spike-rush (Eleocharis compressa var. compressa), a Wisconsin Special Concern plant, is found in moist to wet, often calcareous prairies and mud flats. Blooming occurs early May through early June; fruiting occurs late June through late July. The optimal identification period for this species is late June through late July.

Synonyms: None


  • Distinguishing characteristics: Readily distinguished by its flattened stems, with 9 to 14 vascular bundles.
  • Flower characteristics: Flower head a single spikelet at tip of stem; flowers perfect; sepals and petals absent or reduced to 1-5 bristles; spikelets ovate, 4 to 10 mm long and 3 to 4 mm wide.
  • Fruit characteristics: Achenes yellow-brown, covered with small bumps, somewhat 3-angled; tubercle small, constricted at base.
  • Leaf characteristics: Stems flattened and often twisted, shallowly grooved; sheaths red or purple at base.


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


  • Growth form: Graminoid
  • Vegetative reproduction: Rhizomatous
  • Life cycle: Perennial
  • Comments: Associated Species: Andropogon gerardii, Galium obtusum, Lobelia spicata, Rudbeckia hirta, Senecio plattensis, Sorghastrum nutans, Helianthus 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 Flat-stemmed Spike-rush (Eleocharis compressa var. compressa). 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 Eleocharis compressa var. compressa in the Natural Heritage Inventory Database as of July 2015.

Summary Information
State StatusSC
Federal Status in Wisconsinnone
State RankS2
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 moist to wet, often calcareous prairies and mud flats.
  • Soils: Moist to wet, often calcareous soils.

Natural communities

This table lists the natural communities that are associated with Flat-stemmed Spike-rush. 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
Wet-mesic Prairie 3
Wet Prairie 2
Mesic Prairie 2

Ecological landscapes

This table lists the ecological landscape association scores for Flat-stemmed Spike-rush. 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 broadcast spraying of herbicides; use care with spot spraying.
  • 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.

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.
  • Prescribed burns and/or brushing may be beneficial (dependent on local site conditions).
  • Maintain and restore open habitat through selective clearing and brushing.


Flat-stemmed Spike-rush Photo.

Photo by  staff, Wisconsin DNR.

Flat-stemmed Spike-rush Photo.

As its name suggests, the stems of Eleocharis compressa are distinctively flattened or compressed.

Photo by Ryan O'Connor, 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