Cirsium muticum, also known as swamp thistle, marsh thistle, dunce-nettle, or horsetops, is a North American species of plants in the family Asteraceae, native to central and eastern Canada and the central and eastern United States.

The leaf lobes are often asymmetrical and forked irregularly with the angles containing fine trichomes (multicellular hairs).

[3] The peduncles are 0–15 cm (0.0–5.9 in), each with an inflorescence made up of many tiny florets; the involucre has cobwebby white hairs, and it is often slightly sticky.

In the United States, it grows primarily in the Northeast, the Great Lakes region, and the Appalachians, with isolated populations scattered across the South from Texas to the Carolinas.

[5][6][7] Cirsium muticum is found mostly in alkaline swamps, wetlands, marshes and low forests but some races have been known to grow in wet alpine climates.