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Brook Grass (Catabrosa aquatica)

Life history

Species overview

Brook Grass (Catabrosa aquatica), a Wisconsin Endangered plant, is found in cold springy, sandy areas and in shallow water or mud of streambanks. Blooming occurs throughout July; fruiting occurs throughout August. The optimal identification period for this species is throughout July.

Synonyms: Aira aquatica, Catabrosa aquatica var. aquatica, Catabrosa aquatica var. uniflora


  • Distinguishing characteristics: Loosely clumped or sprawling, creeping bases, rooting at nodes; inflorescence an open pryamid-shaped panicle; spikelets two-flowered; glumes unequal, shorter than the spikelet; lemma smooth, 3 veins parallel to the ragged summit.
  • Flower characteristics: Inflorescence an open, pyramid-shaped or oblong panicle 10 to 20 cm long, erect, yellow-brown, branches spreading in somewhat distant whorls; spikelets mostly 2-flowered or sometimes mostly 1-flowered, the second floret (when present) well above the glumes, short-pediceled.
  • Fruit characteristics: Glumes unequal, shorter than the spikelet, the first glume smaller, 1 to 2 mm long, the second glume ragged at tip; lemma smooth, 3 veins parallel to the ragged summit, 2 to 3 mm long; palea similar to lemma.
  • Leaf characteristics: Blades flat, soft, mostly 10 to 15 cm long and 3 to 10 mm wide; ligule 1 to 4 mm long.


  • Blooming phenology: throughout July
  • Fruiting phenology: throughout August
  • Optimum time to identify: The optimal identification period for this species is throughout July


  • Growth form: Aquatic graminoid-emergent
  • Vegetative reproduction: Stems thick, weak, often horizontal, branching and rooting at nodes in mud or water
  • Life cycle: Perennial
  • Comments: Associated Species: Not recorded for Wisconsin specimens.

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 Brook Grass (Catabrosa aquatica). 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 Catabrosa aquatica in the Natural Heritage Inventory Database as of July 2015.

Summary Information
State StatusEND
Federal Status in Wisconsinnone
State RankS1
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 in cold springy, sandy areas and in shallow water or mud of streambanks.
  • Soils: Wet, sandy soils.

Natural communities

This table lists the natural communities that are associated with Brook Grass. 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
Springs and Spring Runs (Hard) 3

Ecological landscapes

This table lists the ecological landscape association scores for Brook Grass. 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
Western Prairie 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 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

  • Follow BMPs, especially around streams and use care near ravines, steep slopes, cliffs, rock outcrops, etc.
  • 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.


Brook Grass Photo.

Photo © Jose Hernandez.

Brook Grass Photo.

Scanned specimen courtesy of Wisconsin Herbarium

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