C. arvénsis, Hoffm. (Canada Thistle.) Perennial, slender, 1–2° high, the roots extensively creeping; leaves oblong or lanceolate, smooth, or slightly woolly beneath, sinuate-pinnatifid, prickly-margined; flowers rose-purple. (Cirsium, Scop.)—Cultivated fields, pastures, and roadsides, common; a most troublesome weed, extremely difficult to eradicate. (Nat. from Eu.)
80. CÁRDUUS, Tourn. Plumeless Thistle.
Bristles of the pappus naked (not plumose), merely rough or denticulate. Otherwise as in Cnicus. (The ancient Latin name.)
C. nùtans, L. (Musk Thistle.) Biennial; leaves decurrent, sinuate, spiny; heads solitary, drooping; flowers purple.—Fields near Harrisburg, Pa., Prof. Porter. (Adv. from Eu.)
81. ONOPÓRDON, Vaill. Cotton or Scotch Thistle.
Receptacle deeply honeycombed, not setose. Pappus not plumose. Otherwise as Cnicus.—Coarse, branching annuals, or biennials, with the stems winged by the decurrent base of the lobed and toothed somewhat prickly leaves. Heads large; flowers purple. (The ancient Greek name of the plant.)
O. Acánthium, L. Stem (2–4° high) and leaves cotton-woolly; scales linear-awl-shaped.—Roadsides and waste places in the Atlantic States; rather rare. July–Sept. (Adv. from Eu.)
82. CENTAURÈA, L. Star-Thistle.
Heads many-flowered; flowers all tubular, the marginal often much larger (as it were radiate) and sterile. Receptacle bristly. Involucre ovoid or globose, imbricated, the scales margined or appendaged. Achenes obovoid or oblong, attached obliquely at or near the base; pappus setose or partly chaffy or none.—Herbs with alternate leaves and single heads. (Named from the Centaur, Chiron, famous for his skill in healing.)
[*] Achenes terete, 10-dentate; pappus of 10 long bristles and 10 short inner ones.