1. Prenanthes alba L. (white lettuce, rattlesnake root, white snakeroot)
Nabalus albus (L.) Hook.
Pl. 261 a, b;
Map 1090
Stems 30–170 cm
long, usually relatively stout, glabrous or sparsely and inconspicuously
pubescent with short, curled hairs toward the tip, usually purplish-tinged or
with dark purple mottling, often somewhat glaucous. Leaves variable, glabrous
or the undersurface sparsely and inconspicuously pubescent with short, curled
hairs, often somewhat glaucous. Basal and lower stem leaves usually
long-petiolate, the blade 4–30 cm long, usually broadly triangular, sometimes
with a pair of triangular basal lobes, the margins often with few to several
broad, spreading teeth. Median and upper leaves gradually reduced, with
progressively shorter petioles (often sessile toward the stem tip), the blade
entire or nearly so or finely to coarsely toothed or shallowly pinnately lobed,
triangular to ovate or ovate-elliptic. Inflorescences usually elongate
panicles, narrow to broad, the heads tending to be clustered toward the branch
tips, terminal and often also from the upper leaf axils, sometimes with
additional small clusters of heads below the main inflorescence, the heads
commonly nodding. Involucre 10–14 mm long, the inner bracts 7–9(–11), rounded
to sharply pointed at the often somewhat incurved tip, glabrous (the margins
rarely microscopically hairy near the tip), often somewhat purplish-tinged,
appearing somewhat glaucous or minutely pebbled (the effect caused by
microscopic white papillae on the outer surface). Ligulate florets 7–13.
Corollas 9–15 mm long, white to pale pink or lavender, sometimes reddish- or
purplish-tinged toward the base. Pappus 6–7 mm long, orangish brown to reddish
brown. Fruits 4–6 mm long, light brown to yellowish brown. 2n=32. July–September.
Uncommon, known
mostly from historical collections from the northeastern quarter of the state
(northeastern U.S. west to North Dakota and Arkansas;
Canada).
Bottomland forests, mesic upland forests, ledges of bluffs, and banks of
streams and rivers.
As in P.
altissima, some populations in the eastern portion of the range of P.
alba have the pappus straw-colored to light yellow.