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Knotweed Dodder (Cuscuta polygonorum)

Life history

Species overview

Knotweed Dodder (Cuscuta polygonorum), a Wisconsin Special Concern plant, is found in wet-mesic prairies, coastal plain marshes, the margins of commercial cranberry bogs, and, rarely, floodplain forests. Blooming occurs from July through September. The optimal identification period for this species is July through September.

Synonyms: None


  • Distinguishing characteristics: Distinguished from other Cuscuta by its very short styles.
  • Flower characteristics: Inflorescence not rope-like; flowers 4-parted, white; sepals united, subtending bracts absent; petals acutely tipped, at least as long as corolla tube; styles short.
  • Fruit characteristics: Capsule; seed yellow-brown.
  • Leaf characteristics: Alternate, minute scales in place of leaves.


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


  • Growth form: Vine-herbaceous
  • Vegetative reproduction:
  • Life cycle: Annual
  • Comments: Reported parasitizing a wide variety of species including Bidens connata, B. cernua, Polygonum coccineum, Penthorum sedoides, Lycopus americanus, Panicum capillare, Setaria glauca, Polygonum lapathifolium, Rorippa islandica, Hypericum boreale.

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 Knotweed Dodder (Cuscuta polygonorum). 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 Cuscuta polygonorum in the Natural Heritage Inventory Database as of July 2015.

Summary Information
State StatusSC
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 wet-mesic prairies, coastal plain marshes, the margins of commercial cranberry bogs, and, rarely, floodplain forests.
  • Soils: Moist sandy soils.

Natural communities

This table lists the natural communities that are associated with Knotweed Dodder. 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 Knotweed Dodder. 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

  • 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.


Knotweed Dodder Photo.

Photo ©  USDA-NRCS.

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