Swamp Thistle

Cirsium muticum Michx.

Asteraceae (Sunflower Family)

No Photos Yet

Cirsium muticum MIchx., Swamp Thistle: (Bayer Code: CIRMU; US Code: CIMU)

Midwest native biennial thistle that grows 1-7 feet tall, preferring moist soils--wet prairies, marshes, swamps, bogs, open woods
Stems and leaves are mostly green and hairless to moderately hairy; leaf undersides sometimes whitish-green
Leaf outlines mainly oval, with deep lobes; margins have spines at tips of leaf and lobes
Head inflorescences are 0.5-1.5 inch diameter, with purplish-pink ray flowers
Base of head is urn-shaped, and lanceolate, pointed bracts that surround base lack a terminal spine, which separates it from many other thistles
May appear somewhat similar to the following non-native, invasive thistles that also lack spines at tips of bracts surrounding flowering heads:
- Canada thistle (Cirsium arvense), but Canada thistle is a perennial with creeping roots, and Canada thistle, and Canada thistle usually has slightly smaller and more wavy edged leaves, and Canada thistle has found in a wide range of soil types, not just wet soils, compared to swamp thistle
- European Marsh Thistle (Cirsium palustre), but European Marsh Thistle has its flower heads in clusters at the tips of the of stems, and stems are often covered with cobweb-like hairs

(Updated January 24, 2019)