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 aspera Michx. Fl. Bor. Am. 2: 83. 1803. Nabalus asper T. & G. Fl. N. A. 2: 483. 1843.
Scabrous or rough-puberulent; stem virgate, simple, 2°-4° high. Leaves firm, oval, oblong, or oblanceolate, those of the stem all closely sessile, acute or acutish, dentate, denticulate, or the uppermost entire, the lower sometimes clasping, 2'-3' long, 1/2'-1' wide, the basal tapering into winged petioles, commonly obtuse; heads very numerous, erect, spreading, or slightly drooping, 3"-4" broad, 12-16-flowered, in a long narrow thyrsus; involucre oblong, 2"-2i" thick, 5"-7" high, very hirsute, its principal bracts 8-10, with several short outer ones; flowers light yellow; pappus straw-color.
Prenanthes racemosa Michx. Fl. Bor. Am. 2: 83. 1803.
Nabalus racemosus DC. Prodr. 7: 242. 1838.
1: Part 2, 433. 1884.
Stem virgate, rather stout, glabrous and somewhat glaucous; stem striate, 2°-6° high. Leaves thickish, glabrous and glaucous, the lower and basal ones oval, oblong, oblanceolate, or obovate, dentate, denticulate, pinnatifid or pinnately lobed, 4'-8' long, mostly obtuse, tapering into long margined petioles; upper leaves sessile, smaller and partly clasping, lanceolate to ovate-lanceolate, denticulate, entire, or pinnatifid, mostly acute; heads very numerous, erect, spreading, or slightly drooping, 12-16-flowered, 2"-3" broad, in a long narrow thyrsus; involucre oblong-cylindric, hirsute, 5"-6" long, 11/2"-21/2" thick, longer than the hirsute peduncle, its principal bracts 8-10, with several small outer ones; flowers purplish; pappus straw-color.
In moist open places, New Brunswick and Quebec to Maine, Manitoba, Alberta, southern New York, New Jersey, Iowa, Missouri and Colorado. Aug.-Sept.
Prenanthes mainensis A. Gray, from northern Maine and New Brunswick, is probably a hybrid between N. racemosus and N. trifoliolatus.
Prenanthes crepidinea Michx. Fl. Bor. Am. 2: 84. 1803. Nabalus crepidineus DC. Prodr. 7: 242. 1838.
Stem glabrous or very nearly so below, corym-bosely branched and sometimes puberulent above, stout, 5°-9° high. Leaves thin, the basal and lower ones hastate, ovate, oblong, or deltoid, sharply dentate, lobed, or incised, sometimes 10' long, usually with broadly winged petioles; the upper much smaller, sessile or short-petioled, narrowed at the base, not clasping, ovate, deltoid, or lanceolate, acute; heads numerous, pendulous, short-peduncled, corymbose-paniculate, 4"-6" broad, 20-35-flowered; involucre oblong or oblong-campanulate, hirsute, 5"-8" long, about 3" thick, dark green or purplish, its principal bracts 12-15, with several very short outer ones; flowers cream color; pappus brown.
In fields and thickets, western Pennsylvania and New York to Kentucky, west to Minnesota and Kansas. Aug.-Oct.