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..
Annual or biennial, simple or branched, nearly glabrous herbs, with large alternate clasping, sinuate-lobed or pinnatifid, white-blotched leaves, and large discoid heads of purple tubular flowers, solitary at the end of the stem or branches. Involucre broad, subglobose, its bracts rigid, imbricated in many series, the lower ones fimbriate-spinulose at the broad triangular summit, the middle ones similar but armed with huge spreading or recurved spines, the inner lanceolate, acuminate. Receptacle flat, densely bristly. Corolla-tube slender, the limb expanded and deeply 5-cleft. Filaments monadelphous below, glabrous. Anthers sagittate at the base. Style nearly entire. Achenes obovate-oblong, compressed, glabrous, surmounted by a papillose ring. Pappus bristles in several series, flattish, barbellate or scabrous. [St. Mary's thistle.]
A montypic genus of the Mediterranean region.
Stem striate, glabrous or slightly woolly, little branched, 2°-4° high. Leaves oblong-lanceolate, prickly, strongly clasping, the lower often 12' long and 6' wide, the upper much smaller, scarcely lobed, acute; heads about 2 1/2' broad; spines of the middle involucral bracts often 1 1/2' long; pappus bristles white, barbellate.
Escaped from gardens near Kensington, Ontario (T. Walker, according to Macoun), in ballast and waste grounds about the eastern seaports, south to Alabama, and on the Pacific Coast from British Columbia to southern California, where it is naturalized. Virgin Mary's-thistle, lady's-milk, holy thistle. June-Aug.