Caltrop

Tribulus terrestris

Alternative Name(s): Cat-head, Bindii.

Family: Zygophyllaceae

Form: Herb

Origin: Native at least of the Mediterranean, now cosmopolitan. One Australian species is probably included under this name.

Flowers/Seedhead: Solitary in the leaf axils, 5-petalled. Flowers summer and autumn in southern Australia.

Description: Prostrate 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.

Distinguishing features: Distinguished by petals 2–10 mm long; style shorter than to slightly longer than length of stigma and fruit with 2 larger and 2 smaller spines per fruit segment.

Dispersal: Spines of fruit segments ensure rapid dissemination of seeds.

Confused With: Other small-fruited spiny Tribulus species.