Species Profile

Willowleaf Aster

Scientific Name: Symphyotrichum praealtum
Other/Previous Names: Willow Aster,Aster praealtus
Taxonomy Group: Vascular Plants
COSEWIC Range: Ontario
COSEWIC Assessment Date and Status Change: May 2003
COSEWIC Status: Threatened
COSEWIC Status Criteria: Met criteria for Endangered, B1ab(i,iii)+2ab(i,iii), but designated Threatened due to protection within several Windsor Ojibway Prairie Complex sites and adaptability as evidenced in its ability to colonize open disturbed sites within its main area of occurrence around Windsor and therefore not at imminent risk of extirpation.
COSEWIC Reason for Designation: This is a geographically highly restricted species that has undergone range contraction and occurs mainly in fragmented remnant prairie habitats. There are few occurrences and on-going risks from further habitat and population losses due to presence primarily in urbanized centres.
COSEWIC History of Status Designation: Designated Special Concern in April 1999. Status re-examined and designated Threatened in May 2003.
SARA Status: Schedule 1, Threatened
Date of Listing (yyyy-mm-dd): 2005-01-12

Please note that this information is provided for general information purposes only. For the most up to date and accurate list of species listed under the Species at Risk Act, please see the Justice Laws Website.

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Quick Links: | Taxonomy | Photo | Description | Distribution and Population | Habitat | Biology | Threats | Protection | Recovery Initiatives | National Recovery Program | Documents

Image of Willowleaf Aster

Willowleaf Aster Photo 1
Willowleaf Aster Photo 2



There are two varieties of the Willowleaf Aster. The range of the variety praealtum extends into Canada, while the eastern variety angustior is limited to the eastern United States.



The Willowleaf Aster is a fall-flowering, upright perennial that grows from a rhizome (spreading underground stem). The plant can be up to 1.5 m tall, and has a relatively smooth, waxy stem with many leafy flower clusters. The flower heads have 20 to 35 outer florets with pale blue to violet rays; the 20 to 30 central florets have a yellow centre, and the rays become purple with age. The leaves on the upper portion of the stem are narrow and linear, with a few small teeth along the margins; the lowermost leaves have usually fallen off by the time the plant is in flower. The seeds are contained individually within fruiting bodies called achene. When mature, the dry achene fall off the parent plant, and are likely dispersed by the wind.


Distribution and Population

The Willowleaf Aster is common in the Midwestern United States, and reaches the northeastern extent of its range in southwestern Ontario. It is highly localised in Canada, and occurs mainly in two concentrated areas around Windsor and on Walpole Island. There are 13 localities known for the Willowleaf Aster; at least one of these, and perhaps as many as five, have become extirpated. No population trend information is available.



The Willowleaf Aster is found in prairies, meadows, and areas of dense shrubs or small trees throughout its range. In southwestern Ontario, it grows most often in oak savannahs, but is also found in disturbed areas such as roadsides, along railways, and in abandoned fields.



It is difficult for scientists to determine the number of genetic individuals of Willowleaf Aster at a site because the species grows from rhizomes, and forms potentially large, overlapping clones. This aster will also reproduce by setting seed if there are enough genetically different species in the population. Pollen is transferred between individuals by insects - primarily bees, flies, and butterflies.



Many of the known populations occur within the city of Windsor, or on nearby Walpole Island. These areas have been heavily disturbed by industrial activities, house construction, and agricultural practices, and there is potential for further development. Sites observed in 1982 on Walpole Island have been eliminated by house construction. It is also likely that changing drainage patterns at some sites are having a critical impact.



Federal Protection

The Willowleaf Aster is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

In Windsor, a number of populations are protected where they occur within the Ojibway Nature Centre, the Ojibway Prairie Nature Reserves, and the Tall-grass Heritage Park.

Provincial and Territorial Protection

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.


Recovery Initiatives

Status of Recovery Planning

Recovery Strategies :

Name Recovery Strategy for the Willowleaf Aster (Symphyotrichum praealtum) in Canada
Status Final posting on SAR registry



PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.

8 record(s) found.

COSEWIC Status Reports

  • COSEWIC assessment and status report on the willowleaf aster Symphyotrichum praealtum in Canada (2003-12-24)

    Willowleaf aster is an herbaceous, rhizomatous, upright perennial with a relatively smooth and waxy stem growing to 1.5 m tall. The upper stem leaves are generally narrow, linear, with a few small teeth along the margins and lack leaf stalks; the lowermost leaves have usually shriveled and fallen off at the time of flowering. The inflorescence consists of a series of leafy flower clusters with the lowermost branches generally being the longest. The stalks of the flowering heads are moderately to densely hairy. The hairless, leaf-like bracts (phyllaries) surrounding the flower heads are borne in 4-6 strongly graduated series; each has a small, green, diamond-shaped zone towards the tip. The flower heads have 20-35 outer florets with pale blue-violet rays; the central yellow disc florets number 20-30 and become purple with age.

Response Statements

  • Response Statements - Willowleaf Aster (2004-04-21)

    A response statement is a communications document that identifies how the Minister of the Environment intends to respond to the assessment of a wildlife species by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The document provides a start to the listing and recovery process for those species identified as being at risk, and provides timelines for action to the extent possible.

Recovery Strategies

  • Recovery Strategy for the Willowleaf Aster (Symphyotrichum praealtum) in Canada (2017-12-21)

    The Minister of the Environment is the competent minister for the recovery of the Willowleaf Aster and has prepared the federal component of this recovery strategy (Part 1), as per section 37 of SARA. SARA section 44 allows the Minister to adopt all or part of an existing plan for the species if it meets the requirements under SARA for content (sub-sections 41(1) or (2)). The Ontario Ministry of Natural Resources (now the Ontario Ministry of Natural Resources and Forestry) led the development of the attached recovery strategy for the Willowleaf Aster (Part 2) in cooperation with Environment Canada. The Province of Ontario also led the development of the attached Government response (Part 3), which is the Ontario Government’s policy to its provincial recovery strategy and summarized the prioritized actions that the Ontario government intends to take.


  • Order Acknowledging Receipt of the Assessments Done Pursuant to Subsection 23(1) of the Species at Risk Act (2004-04-21)

    This Order acknowledges receipt by the Governor in Council of the assessments of the status of wildlife species done pursuant to subsection 23(1) of the Species at Risk Act (SARA) by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The purpose of SARA is to prevent wildlife species from being extirpated or becoming extinct, to provide for the recovery of wildlife species that are extirpated, endangered or threatened as a result of human activity and to manage species of special concern to prevent them from becoming endangered or threatened.
  • Order Amending Schedules 1 to 3 to the Species at Risk Act (volume 139, number 2, 2005) (2005-01-12)

    Schedule 1, the List of Wildlife Species at Risk of the Species at Risk Act (SARA), is amended by Order of the Governor in Council (GIC), on the recommendation of the Minister of the Environment, by the addition of 73 species. This Order is based on scientific assessments by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and follows consultations with provincial and territorial governments, Aboriginal peoples, stakeholders and the public, and analysis of costs and benefits to Canadians.

Permits and Related Agreements

  • Explanation for issuing permit(#19), persuant to the provisions of section 73 of SARA (2006-06-01)

    Activities may include any of the following for any species: Collection of small amounts of seed (<1%) for propagation ex situ for the pupose of studying seed viability, germination condisions and rates. Collection of a mall proportion (<1%) of inflorescences or flowers for the purpose of determining fertility, seed predation rates, etc. Removal of a small number (<0.1%) of individuals of annual species (e.g. Agalinus spp.) for research on habitat and microsite requirements. Collection of seed for the purpose of propagation ex situ plants to provide material for research and/or for restoration projects. Mapping location, counting and setting up permanent study quadrats may sometime involve accidental trampling of some plants and portions of some habitat. This will be kept to a minimum. Some perturbation of habitat may occur during removal of invasive species. Some experimental purturbation of habitat for restoration purposes may be done in locations where species at risk are thought to be extirpated.

Consultation Documents

  • Consultation on Amending the List of Species Under the Species At Risk Act: March 2004 (2004-03-03)

    The Government of Canada proclaimed the Species at Risk Act (SARA) on June 5, 2003 as part of its strategy for the protection of wildlife species at risk. Attached to the Act is Schedule 1, the list of the species that receive protection under SARA, hereinafter referred to as the 'SARA list'. Canadians are invited to comment on whether all or some of the species included in this document should be added to the SARA list.

Recovery Document Posting Plans

  • Environment and Climate Change Canada's Three-Year Recovery Document Posting Plan (2016-07-06)

    Environment and Climate Change Canada’s Three-Year Recovery Document Posting Plan identifies the species for which recovery documents will be posted each fiscal year starting in 2014-2015. Posting this three year plan on the Species at Risk Public Registry is intended to provide transparency to partners, stakeholders, and the public about Environment and Climate Change Canada’s plan to develop and post these proposed recovery strategies and management plans. However, both the number of documents and the particular species that are posted in a given year may change slightly due to a variety of circumstances. Last update December 2, 2021
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