PROTECTING WISCONSIN'S BIODIVERSITY

 
 
   
 
Scientific Name Common Name Global Rank State Rank Federal Status WI Status

Hill's Thistle (Cirsium hillii)

kk_rd_275.jpg

 

 

 

 

8687.jpg

Photo by Kitty Kohout

 

Counties with Mapped NHI Occurrences

Hill's Thistle (Cirsium hillii), a Wisconsin Threatened species and a Federal Species of Concern, is found in dry prairies and oak barrens. In neighboring states, it is found in pine barrens. Blooming occurs mid-June through early-August, fruiting late-July through late-August. The optimal identification period for this species is mid-June through late-August.

Cirsium pumilum var. hillii, Cirsium pumilum ssp. hillii

 
 
 

Hill's thistle is an erect forb, 30-80cm tall, with a few (1-3), large, solitary flower heads, 3.5-6mm broad, with sweet-scented purple flowers. Flower heads are subtended by 2-5mm long phyllaries (involucral bracts) tipped with a spine. Its foliage and stem are covered in spiderweb-like or short, stiff hairs. It has a hollow taproot and its stem lacks spiny wings on the internodes. Its seeds are usually 4-5mm in length. Leaves are deeply lobed with large and small spines along the edges. The basal rosette and lower cauline leaves are 12-25cm long x 2-7cm wide.

It is distinguished from Cirsium arvense by its basal rosette and long phyllaries, and from C vulgare by its shorter stature and lack of spiny wings on the stem.

Blooming occurs mid-June through early-August, fruiting late-July through late-August.

Perennial. The optimal identification period for this species is mid-June through August.

Associated species include Quercus ellipsoidalis, Pinus banksiana, Andropogon gerardii, A scoparius, Panicum virgatum, Aster species, and Solidago species.

Hill's thistle is found in dry and mesic prairies and oak barrens with dry, sandy soils. In neighboring states it is found in pine barrens.

Avoid known individual plant locations and conduct operations elsewhere when they are least likely to cause damage. Ideally, this would involve frozen, snow-covered ground. However, in areas of the state where frozen conditions are unreliable, very dry soils late in the growing season might be the best available alternative. Consult with a biologist, if needed.

Avoid broadcast spraying of herbicides and use care with spot spraying.

Prescribed burns and/or brushing may be beneficial, dependent on local site conditions and burn frequency. Rotational burns with annual unburned refugia may be preferred.

Maintain and restore open habitat through selective clearing and brushing.

Species of Greatest Conservation Need (SGCN) are associated with habitats (or natural communities) and places on the landscape. Understanding relationships among SGCN, natural communities and ecological landscapes help us make decisions about issues affecting SGCN and their habitat and how to respond. Download the Wildlife Action Plan association score spreadsheet to explore rare species, natural communities and ecological landscape associations

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the Wisconsin Wildlife Action Plan because lack of information can threaten our ability to successfully preserve and care for natural resources.