Carduus muticus (Michx.) Pers.
Cirsium muticum (also known as Swamp Thistle, Marsh Thistle, Dunce-Nettle, and Horsetops) is a biennial dicot that is native to eastern Canada and the United States.
Cirsium muticum is a biennial plant that reaches a height of 180 centimetres (71 in). Its taproot is fleshy and its stem is ridged with hairs toward the base. The leaves are alternate in position, pinnately lobed, and ovate in shape. The leaf lobes are often asymmetrical and forked irregularly with the angles containing fine trichomes (multicellular hairs). The leaves become progressively smaller towards the inflorescence; there are often a few trichomes on the underside. 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. The purple florets can be up to 27 mm (1.1 in) long.
Taxonomy and naming
Distribution and habitat
In Canada, Circium muticum is common in all eastern and Atlantic provinces including Newfoundland and as far west as central Saskatchewan. It is found as far north as Labrador, and in the U.S. its range extends southward along the east coast and west to Louisiana.
Cirsium muticum is as host for some species of butterflies and moths, including the swamp metalmark butterfly (Calephelis muticum), a species that is currently undergoing risk assessment in the United States. The butterfly lays its eggs on the swamp thistle, and when the eggs hatch, the flowers are the only food source for the caterpillars. Species that grow with it include Aster umbellatus (flat-topped white aster), Solidago patula (rough-leaved goldenrod), Lysimachia quadrifolia (prairie loosestrife), and Gentiana procera (smaller fringed gentian).
Swamp thistles can be used to make decorative arrangements. They are often planted in gardens because they are seen as more manageable than other thistles, while still potentially having some anti-herbivory properties.
The plant is not endangered in Canada or the U.S. but it is threatened in the state of Arkansas, and vulnerable in the province of Saskatchewan. Cirsium muticum is at risk primarily because it is a wetland plant, and North American wetlands have been much reduced in extent over the last two centuries.
- C. Frankton & J. Moore (1963). "Cytotaxonomy of Cirsium muticum, Cirsium discolour, and Cirsium altissimum". Canadian Journal of Botany 41: 73–84.
- "PLANTS Profile for Cirsium muticum Michx. (swamp thistle)". United States Department of Agriculture. 2011. Retrieved October 20, 2011.
- John A. Shuey, John V. Calhoun & David C. Iftner (1987). "Butterflies that are Endangered, Threatened, and of Special Concern in Ohio". Ohio Journal of Science 87 (4): 98–106.
- H. Hamilton (2010). "Cirsium muticum Michx., Compositae". Retrieved December 10, 2011.
- "Species: Cirsium muticum". University of Saskatchewan. Retrieved December 10, 2011.
- Morse, K. (2009). "Cirsium muticum –Swamp Thistle". Retrieved 2011-12-15.