Puncturevine (Tribulus terrestris). Also known as goathead, cathead, caltrop, yellow vine, burra gokharu, and bindii. Native to the Old World, this plant is now widely naturalized in the US where it is considered an invasive pest. The spines are strong enough to penetrate the soles of shoes and bicycle tires, and can seriously injure the feet of animals. In traditional Indian and Chinese medicine it has been used as a sexual stimulant, but can be toxic when ingested by sheep. Photo taken near Lee's Ferry, AZ.