3. Cirsium canescens Nutt. (Platte thistle)
Map 1052
Plants biennial
or short-lived perennials, with a long, slender or thick taproot, not suckering
to form clonal colonies. Stems 20–80 cm long, unbranched to several-branched
toward the tip, densely pubescent with persistent white, woolly to felty hairs,
with spiny-margined wings, at least above the midpoint. Basal leaves 10–30 cm
long, 3–6 cm wide, narrowly elliptic to broadly oblanceolate, tapered at the
base, bluntly to sharply angled at the tip, usually with several pairs of
shallow to deep, relatively broad lobes, the margins otherwise toothed or wavy
and spiny, both surfaces appearing grayish or whitish with relatively dense,
woolly hairs, the pubescence sometimes becoming thinner on the upper surface
with age (which appears gray or green). Stem leaves well developed throughout
or progressively reduced above the stem midpoint, the main leaves 4–25 cm long,
narrowly oblong to oblong-elliptic, mostly with shallow (less than 1/3 of the
way from the margin to midrib), irregular lobes or wavy, rounded to a clasping
and strongly decurrent (more than 1 cm) base, otherwise like the basal leaves.
Heads few to several, solitary at the branch tips, appearing sessile or very
short-stalked. Involucre (15–)25–40 mm long, as wide as or slightly wider than
long, usually cobwebby-hairy (from the bract margins), the lower and median
bracts tapered to a loosely ascending to spreading, spiny tip, this 2–4 mm
long, straw-colored to light yellow, also sticky along the midrib. Corollas 20–35
mm long, cream-colored to nearly white, rarely pale pink, the lobes 4–8 mm
long. Pappus 18–30 mm long, usually white. Fruits 5–7 mm long. 2n=34,
36. June–October.
Introduced,
known from a single historical collection from Jackson County (Idaho to South
Dakota south to New Mexico and Nebraska; introduced farther east). Railroads.
The Missouri
specimen of C. canescens was determined as C. undulatum by its
collector, B. F. Bush. In 1951, during his taxonomic and nomenclatural studies of
these two taxa, Gerald B. Ownbey of the University of Minnesota annotated the
sheet as C. canescens but did not cite voucher specimens in his
publication (Ownbey, 1952). Steyermark (1963) overlooked this specimen during
his research for the Flora of Missouri. It resurfaced during the
research of David J. Keil of California Polytechnic State University toward a
treatment of Cirsium for the Flora of North America Project (Flora of
North America Editorial Committee, in press).