Pitcher's Thistle

Cirsium pitcheri

Description

Pitcher's thistle, Cirsium pitcheri, is a perennial herb with a thick, prickly stalk, growing up to 30 in (76 cm) tall. Densely woolly, pale, pointed leaves are deeply divided and attached to the stems by long petioles. Cream-colored or yellowish flowers occur singly or as several heads bunched together on the numerous stem branches. The plant flowers from June until mid-August.

This species reproduces sexually and matures in three to ten years. Seeds are dispersed in a pappus that is picked up and blown by the wind like a parachute. Most seeds settle downwind (inland) from parents, and seedling clusters result when entire seed heads are dispersed as a clump.

Habitat

Pitcher's thistle grows primarily along stabilized sand dunes that line the shores of the Great Lakes, often in "sand blows" or "blowouts." Blowouts are hollows scooped out behind a stable dune by the wind. This species depends on the restless shifting of sands, on an occasional fire, or on scouring waves to maintain and renew its sparse, sand scrub habitat. Later successional stages support dense clumps of dune grasses and woody shrubs that eventually shade out Pitcher's thistle.

Distribution

Pitcher's thistle appears to have originated in the Great Plains area and migrated eastward as the last ice age receded about 8,000 years ago.

When listed in 1988, Pitcher's thistle was found in Michigan at about 100 sites in 25 counties along Lakes Huron, Michigan, and Superior. In Wisconsin, the species was found at eight sites in three counties along the Lake Superior shoreline, and in Indiana, at seven sites along Lake Michigan. It was extirpated from Illinois, but was recently discovered at 12 additional sites in Ontario on the shores of Lakes Huron and Superior. Although seemingly of widespread occurrence, most populations consist of less than 100 plants.

The U. S. Fish and Wildlife Service also lists the species as threatened in Illinois and Ontario, Canada.

Threats

This species is threatened by beachfront development and by increased recreational use of the Great Lakes shoreline. Road and housing construction have permanently destroyed habitat in some places. Dunes have been bulldozed to provide better views from cottages, and some landowners have removed plants, under the impression that it is a "weed." Dune hikers and, more seriously, off-road vehicles have caused serious damage to large portions of the fragile habitat.

Consistently high water levels have inundated habitat in some places—as much as 100 acres (40 hectares) at one locality in Wisconsin.

Conservation and Recovery

The plant is listed as threatened in Indiana, Michigan, and Wisconsin and as rare in Ontario. Populations on public lands—such as the Indiana Dunes (Porter County, Indiana), Sleeping Bear Dunes (Leelenau County, Michigan), and Pictured Rocks National Lakeshores (Alger County, Michigan)—are relatively secure. Recovery efforts are concentrated on acquiring and protecting larger sections of beachfront habitat.

Successful recovery efforts are underway and showing promise. For example, in the spring of 1995, the U. S. Fish and Wildlife Service's Chicago field office assisted the Morton Arboretum in planting Pitcher's thistle seeds and seedlings on an Illinois state nature preserve. More than 1,400 seeds and three greenhouse-raised seedlings were planted. In 1994, two plants in the preserve flowered for the first time, and seeds collected from those flowers were among those planted in 1995. Seedlings emerged from seeds planted in 1994, and by 1995, six plants were blooming.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1 Federal Drive
BHW Federal Building
Fort Snelling, Minnesota 55111
Telephone: (612) 713-5360
http://midwest.fws.gov/

References

Keddy, C. J., and P. A. Keddy. 1984. "Reproductive Biology and Habitat of Cirsium pitcheri. " Michigan Botanist 23: 57-78.

Moore, R. J., and C. Frankton. 1963. "Cytotaxonomic Notes on Some Cirsium Species of the Western United States." Canadian Journal of Botany 41: 1553-1567.

Smith, H. V. 1966. Michigan Wildflowers. Cranbrook Institute of Science, Bloomfield Hills, Mich.

White, D. J., et al. 1981. " Cirsium pitcheri. " In Atlas of the Rare Vascular Plants of Ontario, edited by G.W. Argus and D. J. White. National Museum of Canada.