The Collaborative International Dictionary
bullweed
Knapweed \Knap"weed`\, n. (Bot.) The black centaury ( Centaurea nigra); -- so called from the knoblike heads of flowers. Called also bullweed.
Wiktionary
bullweed
n. knapweed
Usage examples of "bullweed".
Though it was light enough now to make out the fallen bricks, the dun-colored walls with their drifts of piled sand, and the thrusting black spikes of camel-thorn and bullweed against them, there was not yet any sound of birds.
Around the tower, the Citadel lay spread out like a peasant's counterpane of blackish grays and maroons and a dozen faded hues of homespun buff, stitched here and there with the dull green of dusty bullweed and cactus.