Canada-thistle definition

A perennial herb (Cirsium arvense) in the composite family, native to Europe and naturalized as a noxious weed in North America, having spiny-margined leaves and rose-purple or sometimes white flower heads.

A prickly European weed (Cirsium arvense) of the composite family, with heads of purplish flowers and wavy leaves: now common as a fast-spreading, injurious weed throughout the N U.S.

Corn thistle.