This is an introduced species, and although we have it in our area it is not a problem. Some places consider it a noxious weed, The seeds are eaten by the European Goldfinch, and the dried (but very prickly) seed heads are decorative and even used by florists at times. We used to make little mice decorations from them by adding pussy willow eyes and noses on the end.
This picture was taken in Bucks County, Pennsylvania, USA, at Nockamixon State Park on August 6, 2012.
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