Canada Thistle (Cirsium arvense)

Asteraceae or Sunflower Family

Medium tall plant with tattered-looking, spiny leaves.  Flowers purple, rarely white, in small heads.  Seeds spread on dandelion-like down.  Blooms in summer.

A very bad weed from Europe.  Spreads by underground runners, and thus very difficult to eradicate.  Fortunately occurs only in limited patches along the edges of the Park.

Other thistles have fewer, larger flower heads that are, in most cases, spiny like the leaves.