Cirsium muticum Michx.
CC = 10
CW = -5
MOC = 8
Family - Asteraceae/Cardueae
Habit - Usually biennial, with a well-developed cluster of stout, fleshy, white to brown roots (rarely only a single fleshy taproot) in addition to the fibrous roots.
Stem - Erect, to 2.5 m, usually branched, glabrous to sparsely pubescent, lacking spiny wings.
Leaf - Basal and alternate. Basal leaves 15-55 cm long, 6-20 cm wide, ovate to elliptic or obovate, usually tapered at the base and tip, with several pairs of deep lobes, the lobes sometimes irregularly lobed again, the margins otherwise toothed and finely spiny, the upper surface appearing green, nearly glabrous to sparsely pubescent with short, curly hairs, the undersurface appearing green or somewhat whitened, nearly glabrous to sparsely pubescent with cobwebby hairs. Stem leaves progressively reduced from about the stem midpoint, 3-15 cm long, with deep, often relatively narrow lobes, sometimes slightly clasping the stem and minutely decurrent at the base, otherwise like the basal leaves.
Inflorescences - Heads solitary at branch tips, appearing sessile or very short-stalked.
Heads - Involucre 20-35 mm long, as long as or slightly longer than wide, urn-shaped, whitened and cobwebby-hairy, the lower and median bracts tapered to a bluntly or sharply pointed, appressed or ascending tip, this often with a minute, sharp point but lacking a spine, usually also somewhat sticky along the midrib, green with a darker or purplish-tinged area toward the tip.
Ray flowers - Absent.
Disk flowers - All perfect. Corollas 20-32 mm long, reddish purple to dark purple, the lobes 4-8 mm long. Pappus bristles 13-20 mm long, white or slightly grayish-tinged.
Fruits - Achenes 4.0-5.5 mm long.
Flowering - July - October.
Habitat - Fens.
Origin - Native to North America.
Lookalikes - Other thistles within the Cirsium genus.
Other info. - This species occupies a rather specific habitat and is accordingly uncommon in Missouri. It is found in fens located in the southeastern quadrant of the state. Its main range is the northeastern U.S. and Canada. The plants appear similar to other species of thistle, but have involucres which are usually strongly whitened over an underlying purple color. The habitat is also an important factor for identification.
Photographs taken at St. Francois State Park, St. Francois County, MO, 9-24-2010 and 8-26-2015 (SRTurner).