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Water-thread Pondweed (Potamogeton diversifolius)

Life history

Species overview

Water-thread Pondweed (Potamogeton diversifolius), a Wisconsin Special Concern plant, is found in shallow water. Blooming occurs from throughout August. The optimal identification period for this species is mid-July through early September.

Synonyms: Potamogeton capillaceus, Potamogeton capillaceus var. atripes, Potamogeton diversifolius var. multidenticulatus


  • Distinguishing characteristics: Fruit usually with a lateral, entire or toothed ridge on each side of the dorsal keel.
  • Flower characteristics: Spikes dimorphic, with those axillary to submersed leaves globular to ellipsoid, with 1 to 15 flowers on slightly club-shaped peduncles and those axillary to floating leaves more cylindric, sometimes to 3 cm with 5 to 120 flowers, on peduncles 3 to 32 mm.
  • Fruit characteristics: Compressed, 1 to 2 mm, with a minute beak, the entire or toothed dorsal keel usually flanked by a pair of lateral keels that may be represented only by a row of teeth; embryo snail-coiled.
  • Leaf characteristics: Submersed leaves linear to filiform, 1 to 10 cm long by 0.1 to 0.5 mm wide, 1- or 3-veined; floating leaves (not always produced) lance-elliptic to roundish, acute to rounded at each end, 5 to 40 mm long by 2 to 20 mm wide, 3 to 17 veins strongly impressed beneath; stipular sheathes membranous, 2 to 18 mm, free from the 5 to 40 mm petiole.


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


  • Growth form: Aquatic forb-emergent
  • Vegetative reproduction:
  • Life cycle: Perennial
  • Comments: Associated Species: Utricularia sp., Potamogeton sp., Eleocharis smallii.

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 Water-thread Pondweed (Potamogeton diversifolius). 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 Potamogeton diversifolius 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 in shallow water.
  • Soils:

Natural communities

This table lists the natural communities that are associated with Water-thread Pondweed. 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).

Ecological landscapes

This table lists the ecological landscape association scores for Water-thread Pondweed. 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 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

  • This species is likely sensitive to water quality. Following BMPs around streams and buffering associated drainages will reduce eutrophication and prevent water quality degradation.


Water-thread Pondweed Photo.

Photo © Brian Collins.

Water-thread Pondweed Photo.

Photo © Graves Lovell,

Water-thread Pondweed Photo.

Photo © Graves Lovell,

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