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Eastern Mosquito Fern (Azolla caroliniana)

Life history

Species overview

Eastern Mosquito Fern (Azolla caroliniana), a plant, is found in still or slow-moving waters. The optimal identification period for this species is summer through fall.

Synonyms: Azolla filiculoides


  • Distinguishing characteristics: Most likely to be confused with Azolla mexicana, which is generally a bigger plant (1 to 1.5 cm wide) with bigger leaves (1 mm long), and the glochidia have cross-walls.
  • Flower characteristics:
  • Fruit characteristics: A fern, the microspores are contained in massulae 0.3 mm wide. Each massula has a thin wall with glochidia that are without cross-walls.
  • Leaf characteristics: Arranged in rows of 2, the tiny, scale-like leaves are 0.5 mm long and smooth. They have two lobes, the upper 0.5 to 0.6 mm wide and much smaller than the lower, submersed lobe. Branches occur subdichotomously above every third leaf, and the first leaf of a branch holds the sporocarp. Usually green, the leaves turn red by mid-summer.


  • Blooming phenology:
  • Fruiting phenology:
  • Optimum time to identify: The optimal identification period for this species is summer through fall


  • Growth form: Aquatic fern
  • Vegetative reproduction: Broken-off branches will form a new plant
  • Life cycle: Annual
  • Comments:

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

Eastern Mosquito Fern (Azolla caroliniana) is on the "watch list." Watch list species have experienced, or are believed to have experienced, a statewide or range wide decline, but they are not currently tracked in the Natural Heritage Inventory (NHI) database. The watch list includes newly discovered species for which origin and rarity need to be determined, certain animals designated as Species of Greatest Conservation Need (SGCN) in the Wisconsin Wildlife Action Plan, and species that were tracked in the past but proved more abundant, widespread or less vulnerable than previously thought. Although watch list species are not actively tracked by NHI, occurrences documented during surveys are often stored by NHI, as these species could be tracked in the future if there is further evidence of their decline.

Summary Information
State Statusnone
Federal Status in Wisconsinnone
State RankSU
Global RankG5
Tracked by NHIW

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 or slow-moving waters.
  • Soils:

Natural communities

This table lists the natural communities that are associated with Eastern Mosquito Fern. 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

Ecological landscapes

This table lists the ecological landscape association scores for Eastern Mosquito Fern. 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

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.

  • No avoidance measures have been developed for this species.

Management guidance

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

  • No guidance has been developed for this species.


Eastern Mosquito Fern Photo.

Photo © Ann Murray.

Eastern Mosquito Fern Photo.

Photo © John Kohout.

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