This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Prenanthes alba L. Sp. Pl. 798. 1753.
Nabalus albus Hook. Fl. Bor. Am. 1: 294. 1833.
Glabrous and glaucous; stem commonly purple, 2°-s° high. Leaves hastate, ovate, cordate, denticulate, dentate, lobed, or palmately divided, or the upper lanceolate, entire, thicker than those of the preceding species, the larger sometimes 8' long; heads numerous, pendulous, 8-15-flowered, about 3" broad, paniculate, or thyrsoid, and often in axillary clusters; involucre glabrous, or with a few scattered hairs, glaucous, 5"-7" high, about 1 1/2" thick, its principal bracts about 8, purplish, with minute outer ones; flowers greenish or yellowish white, fragrant; pappus cinnamon-brown.
Prenanthes serpentaria Pursh, Fl. Am. Sept. 499. pl.
24. 1814. Nabalus integrifolius Cass. Dict. Sci. Nat. 34: 95. 1825. Nabalus serpentarius Hook. Fl. Bor. Am. 1: 294. 1833.
Glabrous or sparingly pubescent, green; stem stout or slender, not glaucous, 1°-4° high. Leaves rather firm, similar to those of the preceding species, equally variable in outline, pinnatifid or pinnately lobed. palmately divided, or merely dentate, or entire; inflorescence paniculate, the branches divaricate, upcurved; heads numerous, about 3" broad, 8-12-flowered, pendulous, paniculate, and commonly also in axillary clusters; involucre more or less bristly-hispid, rarely glabrous, green or purplish, about \\" thick, 5'-7" long, its principal bracts about 8, shorter than the pappus, with several minute lanceolate outer ones; flowers whitish or cream-color, rarely yellow; achenes about 3" long; pappus light brown or straw-color.
Nabalus cylindricus Small, of the southern mountains, ranging north to Kentucky, differs by an elongated narrow panicle.
Nabalus trifolilatus Cass. Dict. Sci. Nat. 34: 95. 1825. Prenanthes trifoliata Fernald; Brainerd, Jones & Eggles-ton, Fl. Verm. 89. 1900.
Glabrous throughout; stem usually stout, 3°-9° high. Leaves thinnish, the lower long-petioled, usually 3-divided with the divisions stalked or sessile, the upper short-petioled or sessile, all commonly lobed or dentate, but the upper sometimes lanceolate, acuminate and entire; inflorescence paniculate, the panicle-branches ascending, or nearly erect; heads few in the clusters, drooping, 7-12-flowered; involucre pale green or purplish, glabrous, about \\" thick and 6" long, its principal bracts 6-8, equalling the pappus, the short outer ones ovate to lanceolate; flowers whitish or pale yellow; achenes 2"-3" long; pappus light brown.
In woods and thickets, Newfoundland to Pennsylvania, Indiana, Delaware and Tennessee. Aug.-Oct.