5. Cirsium discolor (Muhl. ex Willd.) Spreng. (field thistle)
Pl. 253 d, e;
Map 1054
Plants biennial
or short-lived perennials, often with a slightly thickened taproot in addition
to the fibrous roots. Stems 100–250 cm long, well branched, glabrous or
sparsely pubescent with spreading hairs, sometimes with patches of white,
woolly to felty hairs toward the tip, sometimes appearing slightly glaucous,
without spiny-margined wings. Basal leaves 10–50 cm long, 4–25 cm wide,
narrowly ovate to elliptic or obovate, more or less tapered at the base,
rounded to more commonly bluntly angled at the tip, with several deep lobes,
the margins otherwise coarsely toothed and spiny, the upper surface appearing
green, nearly glabrous to moderately pubescent with stiff, straight hairs, the
undersurface appearing white, densely pubescent with felty hairs. Stem leaves
well developed throughout, the main leaves 4–25 cm long, those toward the
branch tips usually somewhat reduced, with deep (more than 1/2 of the way from
the margin to midrib), narrow to relatively broad lobes, somewhat clasping and
often slightly decurrent at the base, otherwise like the basal leaves. Heads
usually relatively numerous, usually solitary at the branch tips, appearing
sessile or very short-stalked. Involucre 25–35 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 spreading, spiny tip,
this 2–5 mm long, straw-colored to light yellow, usually also somewhat sticky
along the midrib. Corollas 25–32 mm long, usually pinkish purple to reddish
purple, the lobes 6–9 mm long. Pappus 18–25 mm long, white or occasionally
slightly grayish-tinged. Fruits 4.0–5.5 mm long. 2n=20. July–November.
Uncommon in the
Ozark Division, scattered to common elsewhere in the state (eastern U.S. west
to North Dakota and Louisiana; Canada). Upland prairies, glades, tops of
bluffs, openings of mesic to dry upland forests, and less commonly banks of
streams, and bottomland prairies; also fallow fields, old fields, railroads,
roadsides, and open, disturbed areas.
Rare,
white-flowered plants have been called f. albiflorum (Britton) House.
This species is closely related to C. altissimum, but it usually occurs
in more upland habitats than that species and also tends to grow in more
disturbed habitats. The two taxa occasionally hybridize at sites where they
grow together. Dabydeen (1997) studied one such hybrid in eastern Nebraska and
concluded that because the parents have different chromosome base numbers, the
hybrids are sterile. Hybrids (mostly sterile) with C. muticum can also
occur where the two species grow in proximity (Ownbey, 1951), but these have
not yet been reported from Missouri. Steyermark (1963) noted that the young
shoots and leaves have been cooked and eaten.