Prenanthes racemosa
Prenanthes alba
glaucous rattlesnakeroot, glaucous white lettuce, prenanthe à grappe, purple rattlesnake-root
prenanthe blanche, white lettuce, white rattlesnake-root
erect, green or light purple, simple, (stout), glabrous and glaucous proximally, setose or hispid distally.
erect, often mottled purple or nearly all purple (often with stout bases, 8–12 mm diam.), proximally glabrous, tomentulose distally.
proximal usually present at flowering;
petioles broadly winged, (1–15 cm);
blades broadly oblanceolate to spatulate, 4–25 × 1–8 cm, coriaceous, bases attenuate, clasping, margins entire or weakly denticulate, apices obtuse or rounded, faces glabrous;
mid cauline sessile, clasping;
distal sessile and reduced.
proximal present at flowering;
petioles narrowly winged (to 18 cm);
blades usually ovate to triangular or cordate, 4–30 × 3–18 cm, thin to coriaceous, bases often hastate, margins usually coarsely dentate or serrate, sometimes deeply 3-lobed or parted, lobes acute, faces glabrous adaxially, pale to whitish and sometimes hirsute abaxially;
distal reduced.
campanulate, 11–12 × 4–7 mm.
cylindric to campanulate, 13–15 × 3–5 mm.
9–29;
corollas usually pinkish, sometimes white or lavender, 7–13 mm.
7–9(–13);
corollas whitish to pale pink, lavender or red, 9–15 mm.
7–14, green to purple, lanceolate to linear, 10–12 mm, margins scarious, sparsely to densely setose.
(6–)8(–9), ± purplish or maroon, lanceolate, 10–13 mm, margins scarious, minutely ciliate, apices acute, faces glabrous.
of 8, dark green to purple, narrowly triangular-subulate bractlets 2–4 mm, coarsely setose.
of 5–7, triangular to lanceolate bractlets 1–3 mm, glabrous.
(ascending) in (elongate) narrowly racemiform or paniculiform arrays.
(3–8, in clusters) in paniculiform arrays (densest near apices).
golden brown, sub-cylindric, subterete, 5–6 mm, indistinctly 8–12-ribbed;
pappi pale yellow, 6–7 mm.
brown or tan, elliptical to linear, 3.5–6 mm;
pappi usually reddish brown, sometimes rusty, rarely yellowish, 6–7 mm.
= 16.
= 32.
Prenanthes racemosa
Prenanthes alba
Prenanthes racemosa is recognized by its erect, stout, simple habit, glaucous stems, spatulate proximal leaves with broadly winged petioles and rounded to obtuse apices, heads borne in narrow racemiform arrays, purple and hairy phyllaries, and usually pinkish corollas. It is most similar to P. aspera, which differs in its generally smaller stature, more hirsute stems, leaves that are hispid abaxially, proximal leaves usually withered by flowering, and creamy white or yellow corollas. Hybrids between P. racemosa and P. trifoliolata, known as P. ×mainensis, occur in the northeastern United States and southeastern Canada (see discussion under P. trifoliolata).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Prenanthes alba is recognized by the purplish stems, relatively large, coarse, ovate or triangular leaves, relatively long, winged petioles, glabrous and often purple phyllaries, and usually reddish brown pappi. The leaves are variable, occasionally deeply 3-lobed. W. L. Milstead (1964) recognized specimens with a pale yellow pappi as “subsp. pallida,” distributed on the east coast in New Jersey, Virginia, and North Carolina. Because pappus color tends to fade somewhat on herbarium specimens, that character is difficult to assess on older specimens. The name was not validly published.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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