Centaurea calcitrapa.

Centaurea is a genus named for the king of centaurs who was supposed to have discovered
medicinal uses for a plant that came to be called Centaury. Centaurs were presumed to
spend their lives indulging in carnal pleasures, but their king Chiron was wise and kindly.

Calcitro is from Latin "to kick," from which evolved the word "caltrop," a
four-pointed weapon positioned on the ground to impede enemy movements. This
thistle reminds us of that weapon when we try to walk through patches of it.

Compare Yellow Star-thistle (preferred spelling): Centaurea solstitialis.

Solstitialis = "mid-summer."