Species At Risk

Crooked-stem Aster

(Symphyotrichum prenanthoides)


Crooked-stem Aster
Crooked-stem Aster occurrences map


Crooked-stem Aster is a perennial herb. It was named after its zigzagging stems that grow 20 to 90 centimetres tall. The oval-lance-shaped leaves are six to 20 centimetres long, narrow near the base and wider towards the tip. The edges of the leaves are toothed near the tip. The flower heads bloom from August to October and have pale bluish ray flowers and yellow disk flowers which later turn purple or brown.


The Crooked-stem Aster range includes the eastern United States, from New York south to North Carolina and Tennessee, and west to Indiana. There is a separate population in the American Midwest within Wisconsin, Minnesota, Iowa and Illinois. In Canada, the Crooked-stem Aster is only found in southwestern Ontario. About 22 populations were believed to exist in 2002, most of these in Elgin County.


Crooked-stem Aster grows in rich, sandy soil at the edge of forests or in sunny openings within forests. It also grows in wet areas along the banks of rivers and streams, and is sometimes found along roadsides.


The main threat to Crooked-stem Aster is habitat destruction due to clearing of forests, changes to watercourses, and residential or road development. The aster is also vulnerable to invasive plants, such as Garlic Mustard, that compete with it for water, light and space.


The Crooked-stem Aster is protected under Ontario’s Endangered Species Act and the federal Species at Risk Act.

What You Can Do to Help the Crooked-stem Aster

  • The Ministry of Natural Resources tracks species at risk such as the Crooked-stem Aster. You can use a handy online form to report your sightings to the Natural Heritage Information Centre. Photographs with specific locations or mapping coordinates are always helpful. nhic.mnr.gov.on.ca
  • Report any illegal activity related to plants and wildlife to 1-877-TIPS-MNR (847-7667).
  • Private land owners have a very important role to play in species recovery. If you find Crooked-stem Aster on your property, you may be eligible for stewardship programs that support the protection and recovery of species at risk and their habitats.
  • Consult the Ministry of Natural Resources for information on provincial regulations and best management practices when working around wetlands and in forests. Call toll free 1-800-667-1940 or visit the Ministry website at www.mnr.gov.on.ca/en/ContactUs/2ColumnSubPage/STEL02_179002.html.
  • Volunteer with your local nature club or provincial park to participate in surveys or stewardship work focused on species at risk.
  • Pollinators, such as bees, are in steep decline across the globe and they play a key role in the survival of many of Ontario’s rare plants. For information on how you can help scientists monitor pollinator populations in Ontario visit: www.seeds.ca/proj/poll.
  • Invasive species seriously threaten many of Ontario’s species at risk. To learn what you can do to help reduce the threat of invasive species, visit: ontario.ca/invasivespecies ; www.invadingspecies.com ; www.ontarioinvasiveplants.ca ; and, www.invasivespecies.gc.ca .

Did you know?

Bees and butterflies pollinate the flowers of the Crooked-stem Aster. The seeds are scattered by wind after ripening.

Did you know?

Aboriginal people used the Crooked-stem Aster to treat colds and fevers.

The Endangered Species Act

Contact your local ministry office

Often the best source of local information on species at risk is your nearest ministry office. Call with your questions or concerns.