5. Prenanthes racemosa Michx. (rattlesnake root, glaucous white lettuce)
Nabalus racemosus (Michx.) Hook.
Pl. 261 k, l;
Map 1094
Stems 35–170 cm
long, slender to more commonly stout, glabrous or sparsely to densely pubescent
with short, spreading hairs toward the tip, often glabrous below the
inflorescence, often purplish-tinged or with dark purple mottling, glaucous.
Leaves with both surfaces glabrous, glaucous. Basal and lowermost stem leaves
short- to long-petiolate, the blade 4–25 cm long, oblanceolate to obovate, the
margins entire or irregularly toothed, often somewhat crisped or corrugated.
Median and upper leaves gradually reduced, sessile, the blade entire or finely
toothed, obovate to more commonly ovate, oblong-elliptic, or lanceolate.
Inflorescences appearing spicate, as narrowly cylindrical panicles, or as
small, dense axillary clusters of heads along an unbranched main stem, the
heads ascending to spreading or less commonly some of them nodding. Involucre 9–14
mm long, the inner bracts (6–)8(–10), narrowly rounded to more commonly sharply
pointed at the tip, the surface pubescent with relatively coarse, stiff,
spreading to ascending hairs, the margins frequently pubescent with minute,
curled hairs toward the tip, usually dark purple, glaucous, not pebbled.
Ligulate florets 9–16. Corollas 7–15 mm long, pink to lavender or sometimes
white (then often with a purplish-tinged base). Pappus 5–7 mm long, usually
straw-colored. Fruits 5–6 mm long, usually bright yellowish brown. 2n=16.
June–September.
Uncommon, known
only from historical collections from Greene and St.
Louis Counties
(northern U.S. south to Colorado, Kentucky, and New Jersey; Canada). Habitat unknown, but
(according to Steyermark [1963]) possibly “Wet prairies and low ground
bordering streams.”
Plants occurring
to the north of Missouri
with 10–14 (vs. 6–10) longer involucral bracts and 17–26 (vs. 9–16) florets
were segregated by Cronquist (1948) as ssp. multiflora Cronquist.
However, in describing the variation, he noted a broad area of geographic
overlap between the two in which plants of both kinds are routinely encountered
in the same population. Prenanthes racemosa has not been seen in Missouri since the 1890s
and presumably has become extirpated from the state. It strongly resembles P.
aspera. One character that facilitates separation of the two species is
that in P. racemosa the large basal leaves are often persistent at
flowering, whereas in P. aspera the basal and lowermost stem leaves
usually are withered or absent by flowering time.