Cirsium arvense (L.) Scop.
Common Name: CANADA THISTLE, FIELD THISTLE
Coefficient of Conservatism: *
Coefficient of Wetness: 3
Wetness Index: FACU
Physiognomy: Ad P-Forb

Cirsium arvense heads B. S. Walters heads

Found at roadsides, ditches, railroads, fields, clearings, shores; disturbed swampy ground but not usually in very wet places; disturbed sites including filled land, parking areas, utility rights-of-way, dumps, neglected gardens, etc.

Widespread across Eurasia and northern Africa; introduced into North America before 1800. D. Cooley collected Canada thistle in Macomb Co. in 1851, noting “This plant has not yet become troublesome here, but is increasing.” This is a variable species, although most Michigan specimens are the spiny, glabrous var. horridum Wimmer & Grab. as described in the key. A few collections are var. arvense with the upper leaves unlobed and with small spines (up to 2 mm long). We have two collections, from Lenawee Co. (R. W. Smith 747, 4047, MICH), with leaves densely tomentose beneath, at most shallowly lobed, and also with small spines; such plants have been called var. vestitum Wimmer & Grab. White-flowered plants are rare, but have been collected in Baraga, Cheboygan, and Emmet Cos. [f. albiflorum E. L. Rand & Redfield]. This species is dioecious. Plants with only staminate flowers will not produce viable seed (although they may have a reduced pappus).

Locations

Alcona County
Alger County
Allegan County
Alpena County
Arenac County
Baraga County
Barry County
Bay County
Benzie County
Berrien County
Cass County
Charlevoix County
    Including Beaver Island
Cheboygan County
Chippewa County
    Including Drummond Island
Clinton County
Crawford County
Delta County
Dickinson County
Emmet County
Genesee County
Gogebic County
Grand Traverse County
Gratiot County
Hillsdale County
Houghton County
Ingham County
Iosco County
Isabella County
Jackson County
Kalamazoo County
Kalkaska County
Kent County
Keweenaw County
    Including Isle Royale
Lake County
Lapeer County
Leelanau County
    Including Fox Islands
    Including Manitou Islands
Lenawee County
Livingston County
Mackinac County
    Including Bois Blanc, Mackinac, Round Islands
Macomb County
Manistee County
Marquette County
Mason County
Mecosta County
Menominee County
Midland County
Monroe County
Montcalm County
Montmorency County
Muskegon County
Newaygo County
Oakland County
Oceana County
Ogemaw County
Ontonagon County
Oscoda County
Presque Isle County
Saginaw County
St. Clair County
Van Buren County
Washtenaw County
Wayne County

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 14, 2017. http://michiganflora.net/species.aspx?id=284.