Prostrate plant trails up to 2-1/2 feet long, branched from the base and hairy. Spines of fruit are sharp enough to puncture bicycle tires and are painful to bare feet. Can also become embedded in fur and fabric.
Mat-forming annual with diffused, branching stems; leaves opposite, with 3 to 9 pairs of elliptic or oblong leaflets; flowers solitary in axils of leaves, flowers of 5 sepals and 5 pale yellow petals; flowers produce spiny nutlets.
Habitat
Cultivated areas, along roads, disturbed sites.
Flower Characteristics
Solitary flowers in axils of smaller or abortive leaves, stems shorter than the subtending leaf; 5 sepals and 5 pale yellow petals .
Leaf and Stem Characteristics
Leaf is pinnately compound to 2 inches long with leaflets to 1/2 inch long, lowest pair of leaflets unequal in size.
Fruit and Seed Characteristics
Capsules break into 5 spiny nutlets, each with 2 larger spines; after separation the vicious tacklike nutlets land with larger spines upward. Two-spined segment resembles a goat's head with horns.
Nutlets or "seeds" are hard and have a pair of 1/4 inch long sharp spines.