Caltrop (bull's head weed, yellow vine)
Tribulus terrestris

Prostate annual with stems to 2 m long. Leaves with 4–8 pairs of oblong leaflets, each leaflet to 12 mm long, the upper surface dark green and often with hairy margins, the lower surface paler and hairy. Fruit 11–20 mm wide (including spines), comprising a cluster of 5 segments each with 2 larger divergent spines above and 2 smaller downward projecting spines below. Each segment with 1–5 seeds.