Centaurea.

CENTAUREA, L. Several species cultivated, some have become spontaneous. C. benedicta, (Blessed or Lovely Thistle) a good medical plant: leaves, flowers and seeds used, very bitter, somewhat nauseous, tonic and stomachic, sudorific and diuretic, purgative and subemetic, repellent and antacid. Employed in decoction, infusion, extract, for agues, pleurisy, gout, cachexy, anorexia, vertigo, head ache, whooping cough, and even the plague. It is also hepatic, and useful to correct the bile.
2. C. cyanus, called with us Bluebottles, has long been deemed ophthalmic.
3. C. calcitrapa or Knapweed. Root good for nephitis and gravel, in decoction, the analysis gives gum, resin, a green matter, fungine, silica, many salts.
C. jacea, C. nigra, C. solstitialis also spontaneous and more or less equivalents, all called Knapweeds.

Medical Flora, or Manual of the Medical Botany of the United States of North America, Vol. 2, 1830, was written by C. S. Rafinesque.