Cirsium muticum Michx.
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Family: Asteraceae or Compositae
Genus: Cirsium
Species Synonyms: Cirsium muticum var. monticola Fern.
Cirsium muticum var. subpinnatifidum (Britt.) Fern.
Cirsium bigelovii DC.
Carduus muticus (Michx.) Pers.
Common Names: swamp thistle
Canada: Saskatchewan – southern Labrador, Newfoundland, Nova Scotia
Saskatchewan: east-central Saskatchewan; Waskesiu Lake, Tobin Lake, Cumberland Delta, Red River Valley, Upper Assiniboine River
Ecoregion: Aspen Parkland, Boreal Transition, Mid-Boreal Lowland, Mid-Boreal Upland
Saskatchewan: wet woods, clearings, sloughs and lakeshores
Associated Species: black eyed susan, black sanicle, Canada goldenrod, mountain woodfern, tall blue lettuce, white rattlesnakeroot
Provincial Status According
to Harms (2003):
Nature Conservancy Status: G5 S2
Saskatchewan Species at
Risk Status:
COSEWIC Status: None
Swamp thistle is vulnerable because it is somewhat regionally restricted in Saskatchewan. Local populations are usually small. No immediate threats are known for this species.
Height: to 180 cm tall
Roots: taproot fleshy
Stems: biennial, ridged, not winged, multicellular hairs towards the base and beneath head
Leaves: basal and on the stem; basal rosette, stalk winged, leaves, 10 – 25 cm long, 3 – 10 cm wide, lance-shaped, deeply lobed with 4 – 8 pairs of lobes, lobes tipped with short, weak spines; stem leaves alternate, sessile, twice pinnately lobed, yellow conspicuous midvein below, sparsely hairy, margin with yellow spines
Inflorescence: terminal; heads discoid, to 3.5 cm across; bracts in 6 – 8 series, tip blunt or sharp-toothed, tip black to dark brown, midvein dark, woolly; outer bracts 4 – 9 mm long, 2 – 4 mm wide, lacking spine tip, glandular; inner bracts to 15 mm, lance-shaped
Flowers: flowers purple, 20 – 27 mm long, perfect
Fruits: achene 4 – 6 mm long, 1.5 – 2 mm wide, dark brown with yellow rim; pappus 13 – 20 mm, whitish, feather-like
1 Upper leaf surface with yellowish appressed prickles
Cirsium vulgare
1 Upper leaf surface without prickles, may be hairless to woolly
2 Rhizomes creeping; heads unisexual (plants dioecious); bracts 1 – 2 cm tall
C. arvense
2 Stems arise from center of previous year’s rosette; flowers perfect; bracts taller
3 Outer bracts without spine tip
C. muticum
3 Outer bracts with spine tip
4 Middle and upper stem leaves with lobes pointing downwards
C. canescens
4 Middle and upper stem leaves sessile or clasping, if lobes pointing downwards then for < 1 cm
5 Leaves not densely white woolly beneath; inflorescence more compact; bracts lacking sticky dorsal ridge
C. drummondii
5 Leaves densely white woolly beneath; inflorescence loose; bracts with a dark, thickened sticky dorsal ridge
6 Stems green and lightly covered in long, soft hairs, may have multicellular hairs; upper leaf surface green and hairless (or minutely hairy)
C. discolor
6 Stems densely white woolly at least on middle and above; upper leaf surface persistently more or less gray woolly
7 Stem leaves oval to lance-shaped, shallowly lobed to subentire; propagating by shoots from deep tap roots; bracts to 4 cm high
C. undulatum
7 Stem leaves elliptic to inversely lance-shaped, shallowly to deeply lobed; propagating by buds borne on horizontal roots; bracts < 2.5 cm high
C. flodmanii