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Azure Bluets (Houstonia caerulea)

Life history

Species overview

Azure Bluets (Houstonia caerulea), a Wisconsin Special Concern plant, is found in dry prairies and woodlands, as well as damp meadows. Blooming occurs late April through early July; fruiting occurs late May through early August. The optimal identification period for this species is late April through late June.

Synonyms: Hedyotis caerulea, H. caerulea var. faxonorum, Oldenlandia caerulea


  • Distinguishing characteristics: Stems erect; corolla tubes smooth within.
  • Flower characteristics: Sepals narrowly oblong, 1 to 2 mm, acute; corolla typicallly rather light blue-lavender with a pale yellow eye, with a slender tube and an abruptly spreading, flattened limb; corolla tube 5 to 10 mm, smooth within, the limb 10 to 14 mm wide, stamens included; styles of different lengths.
  • Fruit characteristics: Fruit flattened, 3 to 4 mm wide, much broader than long; seeds globular, with a deep round cavity occupying the inner face.
  • Leaf characteristics: Lower leaves oblanceolate to spatulate, 5 to 12 mm, narrowed to a petiole often as long; upper leaves subsessile, oblong-spatulate to linear.


  • Blooming phenology: late April through early July
  • Fruiting phenology: late May through early August
  • Optimum time to identify: The optimal identification period for this species is late April through late June


  • Growth form: Forb-erect
  • Vegetative reproduction: Slender, fragile rhizomes
  • Life cycle: Perennial
  • Comments: Associated Species: Schizachyrium scoparium, Quercus macrocarpa, Lithospermum canescens, Rudbeckia hirta, Sorghastrum nutans, Euthamia graminifolia, Aletris farinosa, Lobelia spicata, Dodecatheon meadia, Polemonium reptans, Phlox pilosa.

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 Azure Bluets (Houstonia caerulea). 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 Houstonia caerulea 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 dry prairies and woodlands, as well as damp meadows.
  • Soils: Moist soils.

Natural communities

This table lists the natural communities that are associated with Azure Bluets. 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
Wet-mesic Prairie 1
Dry Prairie 3
Dry-mesic Prairie 2
Oak Opening 2

Ecological landscapes

This table lists the ecological landscape association scores for Azure Bluets. 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 broadcast spraying of herbicides; use care with spot spraying.
  • Avoid locating landings, staging areas, or access routes in open sandy areas dominated by native grasses.
  • 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

  • Maintain and restore open habitat through selective clearing and brushing.
  • Prescribed burns and/or brushing may be beneficial (dependent on local site conditions).
  • 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.


Azure Bluets Photo.

Photo © Kitty Kohout.

Azure Bluets Photo.

Azure bluets only has one flower per stalk, while the more common long-leaved bluets (H. longifolia) has clusters of usually 3 flowers.

Photo © Jeff Lorch.

Azure Bluets Photo.

Photo © Jeff Lorch.

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