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Twining Screwstem (Bartonia paniculata)

Life history

Species overview

Twining Screwstem (Bartonia paniculata), a Wisconsin Special Concern plant, is found in mucky-peaty sand and boggy-sandy meadows. It is strongly associated with the area covered by Glacial Lake Wisconsin. Blooming occurs July through September; fruiting occurs mid-August through early October. The optimal identification period for this species is late July through mid-September.

Synonyms: None


  • Distinguishing characteristics: Alternate scale-like leaves appressed against the stem; lower leaves may be opposite (leaves on the closely related Bartonia virginica are mostly opposite).
  • Flower characteristics: Inflorescence a raceme; flowers small, 2.5 to 4 mm, white to purplish or yellowish; petals lance-shaped.
  • Fruit characteristics: Capsule.
  • Leaf characteristics: Reduced to scales, which are mostly alternate, with the lower ones opposite.


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


  • Growth form: Vine-herbaceous
  • Vegetative reproduction:
  • Life cycle: Annual/biennial
  • Comments: Associated Species: Rhynchspora capitellata, R. alba, Carex scoparia, C. oligosperma, C. echinata, Pinus banksiana, Drosera rotundifolia, Viola lanceolata, Xyris sp, Juncus dudleyi, Lycopodium inundatum, Muhlenbergia spp, Sphagnum spp, Eriophorum virginicum, Scirpus cyperinus, Osmunda cinnamomea, Vaccinium macrocarpon.

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 Twining Screwstem (Bartonia paniculata). 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 Bartonia paniculata 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 mucky-peaty sand and boggy-sandy meadows. It is strongly associated with the area covered by Glacial Lake Wisconsin.
  • Soils: Wet, acidic, sandy-peaty soils.

Natural communities

This table lists the natural communities that are associated with Twining Screwstem. 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 Twining Screwstem. 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 Plains 3
Northern Lake Michigan Coastal 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

  • Minimize disturbance to hydrology, including soil disturbance from rutting.
  • Survey for and control invasive plants prior to conducting timber operations, as these can be spread by vehicles and often respond vigorously to increased light; see forestry BMPs for invasive species.
  • Prescribed burns and/or brushing may be beneficial (dependent on local site conditions).
  • Maintain and restore open habitat through selective clearing and brushing.


Twining Screwstem Photo.

Photo © Robert Freckmann.

Twining Screwstem Photo.

Twining screw-stem has alternate scale-like leaves and small white to pink flowers.

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