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..
Perennial or biennial, the root thick and deep; stem stout, simple, or little branched, 1 1/2°-2 1/2° tall, densely white-felted. Leaves deeply pinnatifid, white-tomentose beneath, green, loosely tomentose, or glabrate above, the lower 5'-7 long, the lobes lanceolate to oblong, acute, prickly tipped and margined; upper leaves smaller and less divided; heads few, about 2' high and broad; outer bracts of the involucre lanceolate to ovate-lanceolate, firm, dark, tipped with a short weak spreading prickle, the inner linear-lanceolate, unarmed, tipped with a scarious reflexed erose appendage; corolla yellow, its lobes linear; pappus of outer flowers merely barbellate.
Sand hills, Nebraska, Colorado and South Dakota. May-July.
Carduus Flodmani Rydb. Mem. N. Y. Bot. Gard. 1: 451. 1900.
Stem rather slender, 1 1/2°-3° tall, loosely white-cottony, usually more or less branched. Leaves deeply pinnatifid into linear-oblong or lanceolate, acute or acuminate, toothed or entire segments, floccose and green above, densely white-cottony beneath, the lower 6' long or less; heads 1 1/2'-2' broad; involucre campanulate, its linear bracts tipped with yellow prickles; flowers reddish-purple to rose.
Meadows and river bottoms. Iowa and North Dakota to Saskatchewan, Nebraska and Colorado. Has been referred to the western C. canescens. July-Sept.
1: 110. 1849. Cnicus ochroccntrus A. Gray, Proc. Am. Acad. 19:
1892: 336. 1893.
Similar to Cirsium undulatum, but commonly taller and more leafy, often 6° high, equally white-tomentose. Leaves oblong-lanceolate in outline, usually very deeply pinnatifid into triangular-lanceolate, serrate or entire segments, armed with numerous long yellow prickles; lower leaves often 6'-8' long; heads about 2' broad, 1 1/2'-2' high, solitary at the ends of the branches; outer bracts of the involucre lanceolate; tipped with stout yellow prickles of nearly or quite their own length, the inner narrowly lanceolate, long-acuminate; flowers purple (rarely white?).
On plains, Nebraska to Texas, Nevada and Arizona. May-Sept.
Stem densely white-woolly, apparently over 1° high. Leaves linear-oblong to lanceolate, white-woolly beneath, green and sparingly loosely woolly above, irregularly slightly toothed or entire, the upper 3'-6' long, 1/4'-1' wide, the margins prickly; heads solitary, or few, short-peduncled, about 1 1/2 high; outer bracts of the involucre lanceolate, prickle-tipped, the inner narrower with a reflexed acute scarious appendage; pappus bristles of inner flowers plumose, of the outer barbellate.
Western Nebraska and Wyoming. Summer.