1. Cirsium altissimum (L.) Spreng. (tall thistle, roadside thistle)
Pl. 253 a–c; Map
1050
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 10–30 cm long, 4–15 cm wide, narrowly ovate
to elliptic or obovate, tapered at the base, rounded to more commonly bluntly
angled at the tip, unlobed or rarely with several deep lobes, the margins
otherwise toothed or wavy 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, all unlobed or with shallow (less than 1/3 of the way from
the margin to midrib), broad lobes (reduced leaves just below the heads rarely
more deeply lobed), tapered to a slightly expanded and sometimes minutely
decurrent 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 22–32 mm long, usually pinkish purple to reddish purple, the lobes 6–9
mm long. Pappus 17–27 mm long, white or occasionally slightly grayish-tinged.
Fruits 4.5–6.0 mm long. 2n=18. July–October.
Scattered to
common nearly throughout the state (eastern U.S. west to North Dakota and
Texas). Bottomland forests, banks of streams and rivers, and bases of bluffs,
less commonly glades, upland prairies, and openings of upland forests; also old
fields, railroads, and roadsides.
Rare,
white-flowered plants have been called f. moorei Steyerm. See the
treatment of the closely related C. discolor for discussion on
hybridization between the two species and plant uses.