I always think Sowthistles are so beautiful, especially when backlit by the sun. If this is the Perennial Sowthistle (never sure which of two species a flower is), then the Alberta Provincial Designation for this plant is Noxious. Annual Sowthistle is very similar, but reproduces by seed only, and the flowers are smaller than those of Perennial Sowthistle.

www.invasiveplants.ab.ca/factsheets/FS-PerennSowthistle.pdf