6. Cirsium muticum Michx. (swamp thistle)
Pl. 254 a, b;
Map 1055
Plants 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. Stems
40–250 cm long, few- to several-branched, glabrous or sparsely pubescent with
spreading hairs, rarely with patches of white, woolly to felty hairs toward the
tip, not appearing glaucous, without spiny-margined wings. 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, nearly glabrous to sparsely pubescent with
cobwebby hairs. Stem leaves progressively reduced from about the stem midpoint,
3–15 cm long, with deep (more than 1/2 of the way from the margin to midrib),
often relatively narrow lobes, sometimes slightly clasping the stem and
minutely decurrent at the base, otherwise like the basal leaves. Heads usually
relatively numerous, solitary at the branch tips, appearing sessile or very
short-stalked. Involucre (17–)20–35 mm long, as long as or slightly longer than
wide (often appearing broader when pressed), often somewhat cobwebby-hairy, the
lower and median bracts tapered to a bluntly or sharply pointed, appressed or
ascending, nonspiny tip, this often with a minute, sharp point, usually also
somewhat sticky along the midrib, green with a darker or purplish-tinged area
toward the tip. Florets all perfect. Corollas 20–32 mm long, reddish purple to
dark purple (rarely white elsewhere), the lobes 4–8 mm long. Pappus 13–20 mm
long, white or slightly grayish-tinged. Fruits 4.0–5.5 mm long. 2n=20–23,
30. July–October.
Scattered to uncommon
in the eastern portion of the Ozark and Ozark Border Divisions (eastern U.S.
west to North Dakota and Texas; Canada). Fens and less commonly banks of creeks
and bases of bluffs, usually in areas of calcareous seepage.