Zygophyllaceae

Tribulus terrestris

Common Names: Caltrop

Plant Form: Spreading annual herb. Size: Up to 80 cm long. Stem: Reddish-brown to green, many branched, scrambling low to ground. Silvery appearance due to covering of hairs. Leaves: Compound of leaflet pairs, between 4-7 leaflets per leaf, plus single leaf at ends, opposite on stems. Flowers: Bright yellow, 5 petals opening in the morning, which are usually lost quickly, single at leaf junction. Fruit and Seeds: Nearly spherical woody hard burrs to 1 cm long, with sharp rigid spines up to 8 mm long. Break into 5 wedge-shaped nutlets with 2-4 seeds. Habitat: Roadsides, pastures, neglected areas, cropping areas. Distinguishing Features: There are many similar species in the genus Tribulus, and debate over whether many are native. Tribulus minutes and T. micrococus are very similar but much smaller or no spines on the nutlets. Impacts: Spiny fruits can injure stock and humans, damage wool, puncture bike tires, toxic and possibly allelopathic.