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..
Carduus virginianus L. Sp. Pl. 824. 1753.
Cirsium virginianum Michx. Fl. Bor. Am. 2: 90. 1803.
Cnicus virginianus Pursh, Fl. Am. Sept. 506. 1814.
Biennial; stem slender, naked or scaly above, pubescent or somewhat tomentose, simple or branched, 2°-3i° high. Leaves oblong, oblong-lanceolate, or the lowest slightly spatulate, sessile, or somewhat clasping, not decurrent, acute or acutish, spinulose-margined, entire, lobed or pinnatifid into triangular-lanceolate lobes, the lower sometimes 8' long and 2' wide, narrowed into margined petioles, all pubescent or glabrate above, and densely white-tomentose beneath; heads long-peduncled, 1'-1 1/2' broad, about 1' high; outer bracts of the involucre not coriaceous, lanceolate or ovate-lanceolate, tipped with weak short bristles, the inner ones very narrow and merely acuminate; flowers purple.
Biennial, persistently white-tomentose throughout; stem stout, leafy up to the heads, usually branched, 1°-2° high. Leaves sessile, partly clasping or slightly decurrent, pinnately divided into narrowly linear, entire lobed or pinnatifid, acute sparingly prickly segments, 2"-3" wide, with revolute margins; basal leaves often 12' long; heads solitary or several and racemose-spicate at the ends of the branches, about 1 1/2' broad; outer bracts of the involucre ovate-lanceolate, sparingly pubescent and tomentose-ciliate, glutinous on the back, tipped with short spreading bristles, the inner narrowly lanceolate, acuminate or sometimes tipped with weak prickles; flowers cream color.
Shores of Lakes Michigan, Huron and Superior. June-Aug.
Acad. 10: 42. 1874. Carduus undulatus megacephalus Porter, Mem. Torr.
Club 5: 345. 1894.
Biennial, persistently and densely white-tomentose throughout, or the upper surfaces of the leaves at length green and glabrous; stem stout, leafy, usually branched, 1°-3° high. Leaves lanceolate or oblong-lanceolate in outline, acute, sessile or decurrent, or the lowest petioled, undulate, lobed or pinnatifid, the lobes dentate, triangular, often very prickly; basal leaves often 8' long; heads 1 1/2'-3' broad, and nearly as high, solitary at the ends of the branches; outer bracts of the involucre ovate or ovate-lanceolate, firm, glutinous on the back, tipped with short spreading prickles, the inner ones lanceolate, acuminate; flowers purple or pink.
On plains and prairies, Lake Huron to Assiniboia, Alberta, Kansas, New Mexico and Arizona. June-Sept.