4. Prenanthes crepidinea Michx. (rattlesnake root, great white lettuce)

Nabalus crepidineus (Michx.) DC.

Pl. 261 c, d; Map 1093

Stems 100–250 cm long, usually relatively stout, glabrous or sparsely to moderately pubescent with short, curled hairs toward the tip, occasionally also sparsely glandular, often purplish-tinged or with dark purple mottling or spots, not glaucous. Leaves variable, the upper surface often roughened with short, stiff, stout hairs, both surfaces or just the undersurface moderately but inconspicuously pubescent with short, curled hairs along at least the main veins, the undersurface sometimes lighter than the upper surface but not glaucous. Basal and lower stem leaves long-petiolate, the blade 8–30 cm long, broadly ovate to broadly triangular-ovate, usually with 1 or 2 pairs of triangular or ovate basal lobes, the margins usually 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, ovate or oblong-elliptic. Inflorescences usually elongate panicles, relatively 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 12–16 mm long, the inner bracts 10–15, 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 base and occasionally also toward the tip, light green to green, often with a darker green base and/or tip (often darkening further upon drying), not glaucous or pebbled. Ligulate florets (15–)19–27(–38). Corollas 9–15 mm long, greenish yellow to cream-colored or pale yellow, rarely white. Pappus 6–8 mm long, straw-colored to yellowish brown. Fruits 5–6 mm long, yellowish brown to reddish brown. 2n=32. August–October.

Uncommon, known mostly from widely scattered historical collections (northeastern U.S. west to Minnesota and Arkansas). Bottomland forests, mesic upland forests in ravines, banks of streams and rivers, and margins of lakes; also rarely moist depressions along roadsides.

This species can form relatively large colonies of basal rosettes, which are most easily observed in the springtime and that tend to die back by midsummer. Only a small proportion of these rosettes produce flowering stems during any given year. Steyermark (1963) noted the existence of a historical specimen from Greene County that represents a putative hybrid between P. crepidinea and P. aspera. As the two have different ploidy levels, such a hybrid would be expected to be sterile.