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Published In: Flora Boreali-Americana (Michaux) 2: 84. 1803. (Fl. Bor.-Amer.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native

 

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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.

 
 


 

 
 
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