Species Profile

Crooked-stem Aster

Scientific Name: Symphyotrichum prenanthoides
Other/Previous Names: Aster prenanthoides
Taxonomy Group: Vascular Plants
Range: Ontario
Last COSEWIC Assessment: November 2012
Last COSEWIC Designation: Special Concern
SARA Status: Schedule 1, Threatened

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

Image of Crooked-stem Aster

Crooked-stem Aster Photo 1



The Crooked-stem Aster is a perennial herb, 20 to 90 cm tall, with zigzagging stems and pale blue flower heads. It grows in colonies, commonly originating from creeping rhizomes (underground stems that spread horizontally). The Crooked-stem Aster has toothed leaves that vary from oval to lance-shaped. The lower third of each leaf is narrow and without teeth; it expands at the base to clasp the sparsely to densely hairy stem. The number of flower heads on each stem can range from very few to several. Each flower consists of a yellow disc, which turns purple or brownish with age, surrounded by 17 to 30, pale-blue rays that are 7.5 to 12 mm long.


Distribution and Population

In the United States, the Crooked-stem Aster occurs naturally in the Great Lakes Basin, south to Tennessee and North Carolina. It is also present as an exotic (non-native) species in Florida. In Canada, the Crooked-stem Aster is restricted to southwestern Ontario, where it has been found only in Elgin County (multiple populations), and Haldimand-Norfolk Regional Municipality and Oxford County (one population each). A Middlesex County population apparently is extirpated. Twenty-two existing populations of the aster are known, and most average about 20 shoots each. The actual number of plants may be lower, since more than one shoot may arise from one plant. No information on population trends is available for this species in Ontario, but considerable suitable habitat has been lost in the province.



This aster is found along the banks of streams and creeks draining into the north shore of Lake Erie. It prefers rich, sandy, loamy soil, and is usually found at the edge of woods, in partial to full shade.



Population size varies from a few to dozens of scattered individuals. In Ontario, the Crooked-stem Aster blooms from late August to early October. It reproduces primarily by seed, although clones can be formed from elongated, fleshy rhizomes.



The shaded banks of streams and creeks in wooded areas that are home to most populations of Crooked-stem Aster are unsuitable for agriculture. While the plants are not directly threatened by farming, they are vulnerable to selective or clear-cutting of trees for wood. Populations along roadsides are more threatened by habitat modification and loss due to road maintenance and construction, or agriculture on adjacent properties. Significant modifications to stream and river courses, cutting of woodlots, and construction of housing may be the most critical forms of habitat loss for this species.



Federal Protection

More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

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 National Recovery Strategy for the Crooked-stem Aster (Symphyotrichum prenanthoides)
Status Recovery team/planner in place


Recovery Team

Carolinian Woodland Plants Recovery Team

  • Jarmo Jalava - Chair/Contact - Other
    Phone: 705-760-2823  Send Email



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.

10 record(s) found.

COSEWIC Status Reports

  • COSEWIC Assessment and Status Report on the Crooked-stem Aster Symphyotrichum prenanthoides in Canada (2013)

    Crooked-stem Aster (Symphyotrichum prenanthoides) is a perennial wildflower up to 90 cm tall with pale blue flower heads and zigzagging stems. The leaves become narrowed in the lower third but expand at the base to clasp the stem. The species grows in colonies, with multiple stems arising from creeping rhizomes (horizontal underground stems). Each flower head consists of a yellow disc, surrounded by 17 to 30, pale blue rays. Canadian populations of Crooked-stem Aster occur in the Carolinian Forest Region at the northern limit of the species’ range. They may be genetically isolated from other populations and have unique adaptations that contribute to their significance for conservation.

COSEWIC Assessments

  • COSEWIC Assessment - Crooked-stem Aster (2002)

    Designated Special Concern in April 1999. Status re-examined and uplisted to Threatened in May 2002. May 2002 assessment based on new quantitative criteria applied to information from the existing 1999 status report.

Response Statements

  • Response Statement - Crooked-stem Aster (2013)

    This perennial aster is restricted in Canada to a small area of the Carolinian forest near the shore of Lake Erie in Ontario. The species has experienced historic declines, but no recent losses have been documented and overall numbers appear to be stable. Invasive plants occur at a number of sites and have the potential to negatively impact the species in the future. Additional threats include indirect impacts of Emerald Ash Borer, and roadside maintenance. The species has a restricted distribution in Canada, and its persistence will likely require ongoing monitoring and management of invasive species.
  • Response Statements - Crooked-stem Aster (2004)

    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.


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

    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 (2005)

    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.

COSEWIC Annual Reports

  • COSEWIC Annual Report – 2012-2013 (2013)

    Under Canada’s Species at Risk Act (SARA), the foremost function of COSEWIC is to “assess the status of each wildlife species considered by COSEWIC to be at risk and, as part of the assessment, identify existing and potential threats to the species”. COSEWIC held two Wildlife Species Assessment Meetings in this reporting year (October, 2012 to September 2013) from November 25 to November 30, 2012 and from April 28 to May 3, 2013. During the current reporting period, COSEWIC assessed the status or reviewed the classification of 73 wildlife species. The wildlife species assessment results for the 2012-2013 reporting period include the following: Extinct: 0 Extirpated: 2 Endangered: 28 Threatened: 19 Special Concern: 19 Data Deficient: 4 Not at Risk: 1 Total: 73 Of the 73 wildlife species examined, COSEWIC reviewed the classification of 50 species that had been previously assessed. The review of classification for 26 of those species resulted in a confirmation of the same status as the previous assessment.

Consultation Documents

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

    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.
  • Consultation on Amending the List of Species under the Species at Risk Act: Terrestrial Species – December 2013 (2013)

    The Government of Canada is committed to preventing the disappearance of wildlife species at risk from our lands. As part of its strategy for realizing that commitment, on June 5, 2003, the Government of Canada proclaimed the Species at Risk Act (SARA). Attached to the Act is Schedule 1, the list of the species provided for under SARA, also called the List of Wildlife Species at Risk. Endangered or Threatened species on Schedule 1 benefit from the protection of prohibitions and recovery planning under SARA. Special Concern species benefit from its management planning. Schedule 1 has grown from the original 233 to 518 wildlife species at risk. Please submit your comments by March 23, 2014, for terrestrial species undergoing normal consultations and by October 23, 2014, for terrestrial species undergoing extended consultations. Consultation paths.

Recovery Document Posting Plans

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

    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 22, 2016