Xanthium spinosum
A branched annual with smooth green or yellowish stems which are armed with 3-pronged spines. The blue-green leaves are densely white woolly below. The fruits are burs, ~ 10mm long, with reddish hooked spines.
Photo by S. Neser (1985-05-20) courtesy Ecoport
(source URL: http://www.ecoport.org)