Kendall County (IL) Forest Preserve District

 Swamp Thistle
Cirsium muticum   [C-value 10]
Aster family (Asteraceae)
 Blooms August - Mid-October

The native Swamp Thistle is uncommon in our area. It prefers full sun and wet to moist soil and might be found in fine marshes and fens. This biennial forms a rosette of basal leaves the 1st year followed by a flowering plant (2-7' tall) the 2nd year. The basal leaves are typically 8" long and 3" across. The 2nd year plant has slender ridged stems with alternate deeply-cut spine-tipped leaves up to 10" long and 4" across. The upper stems terminate in 1-5 elegant pinkish to lavender flowerheads about 1¼-2" across having a dense cluster of numerous disk florets and no ray florets. The corollas of the disk florets are narrowly cylindrical below, becoming slightly wider above with 5 narrow lobes.

 

 

 

Swamp Thistle in lower fen at Lyon Forest Preserve September 4, 2013

 

 

 

 

 

 

 

 

 

 

 

Swamp Thistle foliage in lower fen at Lyon Forest Preserve September 4, 2013

 

 

 

 

 

 

 

 

 

 

Swamp Thistle in lower fen at Lyon Forest Preserve August 8, 2017

 

 

 

 

 

 

 

 

 

 

 

Swamp Thistle in lower fen at Lyon Forest Preserve August 8, 2017 (upper foliage)

 

 

 

 

 

 

 

 

 

 

 

 

Swamp Thistle winter seedheads in fen at Lyon Forest Preserve November 20, 2014

 

 

 

 

 

 

 

 

 

 

 

Swamp Thistle winter stem in fen at Lyon Forest Preserve November 20, 2014

 

 

 

 

 

 

 

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