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Caltrop Vine
Puncture Vine

Tribulus terrestris

Photo © by Michael Plagens

Image taken May 8, 2005 Phoenix, Maricopa Co., Arizona.

maturing fruit of puncture vine, Tribulus terestris

Close-up of the sharply thorned fruit which are sometimes referred to as Goat's Head or Caltrop. Scale is in millimeters. A shizocarp, the fruit will split into five seeds; note that two seeds will be smaller than the others.

If you ride a bicycle it is wise to learn to recognize this distinctive plant. It grows prostrate on the ground with shiny, dark green, compound leaves and has five-pointed, bright yellow flowers. What is often not obvious from the height of a bicycle are the extremely sharp and sturdy seeds with points arranged in a tetrahedron. There is a similar man-made device known as a caltrop which was made from wood or metal and deployed in wartime as a defense against cavalry or track vehicles. The tetrahedron shape means that a sharp point is oriented upward at all times. Caltrop Vine seeds lie ready and waiting to be carried away in a tire, shoe or bare foot.

Microlarinus weevil larva in seed of puncture vine

When broken open seeds containing weevils will have a brown, hollowed-out center and the small cream-colored larva (grub)of Microlarinus lareyniei may be present.

This relative of the creosote bush, native to North Africa, was likely dispersed to the Southwest via the hooves of horses carrying early Spanish Conquistadores or missionaries. A couple of weevil species from India have been introduced as biological control agents, but my observation is that the weevils are heavily parasitized by wasps and as a result are not so effective in reducing puncture vine populations.

Zygophyllaceae -- Caltrop Family

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