Cirsium pumilum var. hillii (Hill's Thistle)
|Also known as:||Hollow-root Thistle|
|Habitat:||sun; open fields, prairies, sandy soil|
|Bloom season:||June - August|
|Plant height:||1 to 2 feet|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Bracts are generally long and narrow, tipped with a slender erect to spreading spine and fine cobwebby hairs around the edges, often becoming smooth with age. Like most native thistles it has a white stripe up the center of the bract.
Leaves and stem:
Leaves are lobed with wavy edges, oblong to elliptic, mature leaves 6 to 8 inches in length. Both stems and undersides of leaves are densely woolly with a whitish appearance but not sharp. Leaf edges have short, dense spines. Stems are stout, often single or lightly branched. It is also noted to have thickened, hollow roots.
Minnesota's least common, and certainly spiniest, native thistle, its continental range is also smaller than most related native thistles. Like many prairie species, populations across its range have declined due to habitat loss primarily from agriculture and commercial development. According to the DNR, it was listed it as a Minnesota Special Concern species in 1984. Its often short stature makes it difficult to detect at a distance and so one often stumbles upon it right under foot. The blooms are typically around 2 inches across but can reach a diameter of 3 inches. It is truly a spectacular sight to come across such a bloom. Hill's Thistle often goes by Latin name Cirsium hillii but it is now treated as a variety of Cirsium pumilum (Pasture Thistle), var. hillii, with var. pumilum a more eastern species.
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- Hill's Thistle plant with 3-inch flower head
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Photos by K. Chayka taken at Lost Valley SNA in Washington County, Ordway Prairie in Pope County, and along Hwy 64 in Cass County. Photos courtesy Peter M. Dziuk taken at Gray Cloud Island SNA, Dakota County.
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