A close up of the Canada thistle.
Canada thistle definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
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.
Canada thistle definition by American Heritage Dictionary
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.