This plant forms a bush 3 feet tall and about 3 feet wide. 8 - 10 inch long leaves grow from the base and 6 - 10 flower stalks grow to about 3 feet tall usually bearing only one yellow globe or pompom flower 3 inches in diameter. The attached picture was taken in mid July.
Giant Knapweed Centaurea macrocephala. http://ip30.eti.uva.nl/BIS/flora.php?selected=beschrijving&menuentry=soorten&id=3881
Don't know about BC but WA is prohibiting this plant, based on an extensive patch that arose in Whitman (I think) Co.