C. nutans: biennial; stems erect, cottony, 2-3 feet high; leaves deeply pinnatifid, very prickly, their edges decurrent along the stem, forming narrow very prickly wings; flower-heads large and drooping, crimson, solitary or 3-4 in a loose corymb; involucral bracts numerous, with a stiff, narrow-lanceolate appendage, ending in a spreading prickle. - Musk Thistle. - Waste places. Fl. July, August.
C. acanthoides much resembles this, but is usually taller and rather more branched; the leaves narrower and more prickly; the stem more thickly covered with prickly appendages, decurrent from the base of the leaves; the flower-heads smaller, globular, drooping; and the numerous narrow involucral bracts ending in a linear, spreading prickle.
C. lanceolatus; biennial; stems stout, 3 - 4 feet high, winged and prickly; leaves waved pinnatifid, with short narrow lobes, the terminal one longer and lanceolate, all ending in a stiff prickle, rough above, with short almost prickly hairs, white and cottony beneath; flower-heads few, ovoid, the involucni bracts lanceolate, cottony, ending in a stiff, spreading prickle; florets purple. - Fields, pastures, and waste places. Fl. June to September.
C. palustris: annual or biennial; stems stiff, scarcely branched, 4-5 feet high, quite covered with the prickly de-current margins of the leaves; leaves long, narrow, pinnatifid with numerous ovate wavy prickly lobes, and a few rough hairs scattered on both surfaces; flower-heads numerous, small, ovoid, usually collected in clusters, forming an irregular terminal corymb; involucral bracts numerous, with very small somewhat prickly points, the inner ones often coloured; florets purple. - Wet fields and meadows. Fl. July, August.
†† Leaves sessile or very partially decurrent.
C. arvensis: stems erect, 3-4 feet high; leaves narrow, pinnatifid, very prickly, either embracing the stem with prickly auricles or shortly decurrent; flower-heads in loose terminal corymbs, dioecious; the males nearly globular, with projecting purple florets, the females with much longer involucres and shorter florets; involucral bracts numerous, appressed, with small prickly points. - Cultivated and waste places. Fl. July.
C. heterophyllus: stems stout, 3-i feet high, deeply furrowed, with a little loose cottony wool, not prickly; leaves clasping the stem, with scarcely decurrent auricles, lanceolate, glabrous above, cottony white beneath, bordered with small, bristly but scarcely prickly teeth, sometimes slightly lobed; flower-heads large, growing singly on long peduncles; involucral bracts glabrous, lanceolate, obtuse, or with a very minute not prickly point. - Mountain pastures. Fl. July, August.
C. pratensis: stems 1-2 feet high, usually simple, with a single ovoid flower-head, or occasionally divided into 2-3 long one-headed branches; leaves sinuate or shortly pinnatifid, the stem-leaves lanceolate, bordered with short, slightly prickly teeth; heads somewhat cottony; involucral bracts lanceolate, attenuate, appressed. - Wet meadows and pastures. Fl. June. This plant is sometimes regarded as a variety of C. tube-rosus. Luxuriant specimens, with more divided leaves, sometimes slightly decurrent, have been named C. Forsteri.