Species At Risk

Hill’s Thistle

(Cirsium hillii)


Hill’s Thistle
Hill’s Thistle occurrences map


Hill’s Thistle is a perennial thistle that reaches a height of 25 to 60 centimetres. The stems are soft and covered with fine hairs. It has a few smooth or slightly hairy leaves that taper to the tip and are shallowly lobed. A few branches near the top of the stem produce one or several large flowering heads that contain many tiny pink-purple (rarely white) flowers. At the base of the plant there is a flat spiral of long oval-shaped leaves.


Hill’s Thistle is only found near the Great Lakes of North America. In Canada, following an assessment in 2004, Hill’s Thistle is believed to persist at 64 sites in southern Ontario. It is mainly found on Manitoulin Island, and on the west side of the Bruce Peninsula.


In Ontario, Hill’s Thistle is found in open alvar grasslands, surrounded by forests of Jack Pine, White Spruce, and Eastern White Cedar. Alvars are flat areas of limestone bedrock with very shallow soil and vegetation consisting of scattered trees, shrubs and grasses. This sun-loving thistle is also found in prairie and sand dunes. These are all rare habitats in Ontario, characterized by open and sunny conditions.


The main threat to Hill’s Thistle in Ontario is the lack of suitable habitat. Hill’s Thistle prefers sunny sites, especially openings in woodland, but these habitats are undergoing natural succession (a series of predictable changes over time in the kinds of plants growing in an area) as shrubs and trees gradually invade open areas.

Wildfires can be used to create open habitats suitable for Hill’s Thistle by limiting natural succession. Today, most areas are managed for fire. As a result, many of the open areas where Hill’s Thistle grows are reverting to woodland and becoming too shaded. Hill’s Thistle is often found growing close to shoreline areas, and these areas are prime sites for cottage development. Other human activities, such as quarrying and ornamental stone removal, ATV traffic and physical trampling, also pose threats.


Hill’s Thistle is protected under Ontario’s Endangered Species Act and the federal Species at Risk Act.

What You Can Do to Help Hill’s Thistle

  • The Ministry of Natural Resources tracks species at risk such as Hill’s Thistle. 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 Hill’s Thistle on your property, you may be eligible for stewardship programs that support the protection and recovery of species at risk and their habitats.
  • Hill’s Thistle 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.

Did you know?

Hill’s Thistle grows on alvars - one of the rarest habitats in North America. These barren-looking landscapes of exposed bedrock support an amazing diversity of plants and insects.

Did you know?

In Ontario, Hill’s Thistle often grows with other species at risk such as Lakeside Daisy and Houghton’s Goldenrod.

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.