thistles Definition

any of various prickly composite plants (especially genera Carduus, Cirsium, and Onopordum) with often showy heads of mostly tubular flowers; also : any of various other prickly plants

a biennial Eurasian thistle (Cirsium vulgare) with purplish flower heads and prickly leaves that is naturalized as a weed in the U.S.

a European thistle (Cirsium arvense) with pinkish-purple or white flowers naturalized as a weed in North America

any of a genus (Echinops) of widely cultivated Asian and Mediterranean composite herbs with spiky globose blue or white flowers

a tall thistle (Silybum marianum) having white-veined dark green leaves and large purple flower heads that is native to the Mediterranean region but has become naturalized elsewhere including the U.S.; also : an extract of milk thistle and especially its seeds that is held to protect the liver from damage or disease

a Eurasian thistle (Carduus nutans) that has nodding musky flower heads and is naturalized in eastern North America

any of a genus (Sonchus) of spiny weedy Eurasian and African composite herbs including some (such as S. arvensis and S. oleraceus) widely naturalized in North America

a widely naturalized spiny Old World knapweed (Centaurea calcitrapa) with purple flowers —called also caltrops

any of various knapweeds related to the star thistle