Black Knapweed, the Centaurea nigra, is a common tough-stemmed composite weed growing in our meadows and cornfields, being well known by its heads of dull purple flowers, with brown, or almost black scales of the outer floral encasement.
Knapweed is popularly called Hard heads, Loggerheads, Iron heads, Horse knob, and Bull weed.
Dr. Withering relates that a decoction made from these hard heads has afforded at least a temporary relief in cases of diabetes mellitus, "by diminishing the quantity of urine, and dispelling the sweetness."
Its chief chemical constituent enicin, is identical with that of the Blessed thistle, and the Blue bottle, and closely resembles that of the Dandelion. It has been found useful in strengthless indigestion, especially when this is complicated with sluggish torpor of the liver. From half to one ounce of the herb may be boiled in eight fluid ounces of water, and a small wineglassful be taken for a dose twice or three times a day. In Bucks young women make use of this Knapweed for love divination:—
"They pull the little blossom threads