Goathead Thorn: Last but Not Least of the Evil Plants

We human beings are rather smug about our accomplishments. That's why it's always so devastating when nature shows it can beat us, and easily.

I realized this some years ago when a mere plant seed punctured my son's bicycle tire.

My son was riding his bike at the school playground, and when he came home, pointed out that he had a flat tire. I was puzzled, but we had the tire fixed. Then the following week it happened again.

It was the fault of a little plant that I didn't even know existed, the goathead thorn (Tribulus terrestris).

Also known as puncture vine, caltrop, bull's head, and Texas sandbur, this weed came to California sometime in the early 20th century from Eurasia and Africa, probably attached to the wool of imported sheep. California is now one of the worst infested states, along with Arizona, New Mexico, Nevada, Oregon, and Texas.

Goathead thorn is a little low-growing weed, so flat to the ground that you might not even notice it unless you were looking for it. Rather deceptive, because if it weren't for the seeds, you would completely overlook it.

The seed case does look a little like the shape of a goat's head. That is, if the goat's head had big spikes sticking out of it.

It's about the nastiest, sharpest thorny thing I've ever seen. In addition to being able to pierce bicycle and auto tires, the seed spikes can injure people, pets, and livestock.

Goathead thorn is a problem throughout the Western United States. It is especially a problem for ranchers, who must deal with sheep, cattle and horses who are injured by the thorns, either by eating them or stepping on them.

One little goathead plant can produce up to 5,000 seeds a year. The seeds persist in the soil for as long as 20 years, making it very hard to completely eliminate it.

Farmers and ranchers really hate goathead thorn. The plants compete with crops for water. And the sharp seed burrs are very bad for livestock, since the spines can puncture their mouths, digestive tracts, and feet. The plants are also toxic to grazing animals, particularly sheep.