"Canada thistle." YourDictionary, n.d. Web. 12 October 2018. <http://www.yourdictionary.com/canada-thistle>.
Canada thistle. (n.d.). Retrieved October 12th, 2018, from http://www.yourdictionary.com/canada-thistle
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.