Species At Risk

Willowleaf Aster

(Symphyotrichum praealtum)


Willowleaf Aster
Willowleaf Aster occurrences map


The Willowleaf Aster is a perennial herbaceous plant that blooms in autumn. It has a fairly smooth, waxy stem that can reach up to 1.5 metres in height. The small daisy-like flowers have pale blue-violet petals and a yellow centre that turns purple with age. The upper leaves are narrow and grass-like with a few small teeth along the edge. The tiny seeds are scattered by the wind.

Action we are taking:


In Canada, the Willowleaf Aster is believed to exist at about 12 locations in southwest Ontario, in Lambton, Essex and Middlesex Counties and the Municipality of Chatham-Kent. Additional populations may no longer exist. The largest populations are in the greater Ojibway Prairie Complex of Windsor and on Walpole Island. The population size is unknown. The Willowleaf Aster is common in the Midwestern United States.


In Ontario, the Willowleaf Aster is found in openings of oak savannahs, a very rare type of vegetation community containing many tallgrass prairie herbs and oak trees. It has also been found along railways, roadsides and in abandoned farm fields.


The main threat to Willowleaf Aster is habitat destruction due to habitat alteration, urban, and industrial development. In the last 20 years, urban expansion has caused this rare plant to disappear from several sites where it was once found.

Fire is essential to maintain a healthy prairie and savannah ecosystem, so the absence of regular fire is also a threat to this plant.


Willowleaf Aster is protected under Ontario’s Endangered Species Act and the federal Species at Risk Act.

What You Can Do to Help the Willowleaf Aster

  • The Ministry of Natural Resources tracks species at risk such as the Willowleaf 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 Willowleaf Aster on your property, you may be eligible for stewardship programs that support the protection and recovery of species at risk and their habitats.
  • Willowleaf Aster and many other species at risk depend on healthy grassland prairies, a very rare habitat in Ontario. Learn more about these habitats, the species that depend on them, and what you can do to help at www.tallgrassontario.org.
  • 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?

Aboriginal people used Willowleaf Aster to treat stomach aches and injuries. They also smoked the dried leaves for good luck while hunting.

Did you know?

The Willowleaf Aster is much more common in the United States, where it provides nectar (an important food source) for migrating Monarch butterflies.

Did you know?

The seed produced by the Willowleaf Aster has a low germination rate, but the plant is very successful in spreading by underground roots called rhizomes. In fact, many clusters of this plant, with sometimes 100 or more stems each, may actually be a single plant.

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.