What may look like purple fringing are the tips of the not-yet-opened purple petals. I do not know whether globe thistles belong to the family of thistles; for me they rather look like flowering garlic or onions I don't consider them weed but a decorative garden plant. -Gerald
Thanks, Michael, shu and Paul. Paul, this is a globe thistle (Wikipedia told me it is called echinops in latin), it is much bigger than clover. -Gerald