2. Prenanthes altissima L. (rattlesnake root, tall white lettuce)

P. altissima var. cinnamomea Fernald

Nabalus altissimus (L.) Hook.

Pl. 261 e–g; Map 1091

Stems 30–250 cm long, slender to stout, glabrous or sparsely and inconspicuously pubescent with short, curled hairs toward the tip, often purplish-tinged or with dark purple mottling or spots, sometimes somewhat glaucous. Leaves variable, glabrous or the undersurface sparsely and inconspicuously pubescent with short, curled hairs, the undersurface pale but not glaucous. Basal and lower stem leaves long-petiolate, the blade 4–20 cm long, broadly ovate to broadly triangular or less commonly somewhat heart-shaped, usually with 1 or 2 pairs of triangular or ovate basal lobes, the margins often with few to several often irregular, broad, spreading teeth or less commonly shallow lobes. Median and upper leaves gradually reduced, with progressively shorter petioles (usually short-petiolate toward the stem tip), the blade entire or more commonly finely to coarsely toothed or shallowly pinnately lobed, sometimes even those of the upper leaves deeply 3-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 9–14 mm long, the inner bracts 4–6, rounded to sharply pointed at the often somewhat incurved or outcurved tip, glabrous (the margins rarely microscopically hairy near the tip), pale green with a darker green base (this often darkening further upon drying), not glaucous or pebbled. Ligulate florets 4–6. Corollas 7–15 mm long, greenish yellow to cream-colored or pale yellow, sometimes appearing nearly white. Pappus 5–6 mm long, orangish brown. Fruits 4–5 mm long, light brown to yellowish brown. 2n=16. July–October.

Scattered, mostly in the Ozark and Ozark Border Divisions (eastern U.S. west to Michigan, Missouri, and Texas; Canada). Swamps, bottomland forests, mesic upland forests in ravines, banks of streams and rivers, and bases and ledges of bluffs; also rarely pastures.

This species is quite variable in different portions of its range. Some eastern populations have much more hairy stems and have been called var. hispidula Fernald. The pappus is typically straw-colored to light yellow in the eastern portion of the range but gradually deepens in color farther west. In the western part of the range, including Missouri, the pappus is a uniform cinnamon color. Such populations have been treated as var. cinnamomea by some botanists (Steyermark, 1963). Prenanthes altissima is often observed in the springtime as rosettes of usually 3-lobed leaves. By midsummer, in most cases the leaves will have died back for the year, with only a few individuals producing flowering stems.