The Goathead (Tribulus_terrestris)

Here is the ultimate goathead (or tackweed) blog post. From Wikipedia and featuring local photography, we have the goathead:

http://en.wikipedia.org/wiki/Tribulus_terrestris

Wikipedia Entry: Goathead

Tribulus terrestris is a flowering plant in the family Zygophyllaceae, native to warm temperate and tropical regions of the Old World in southern Europe, southern Asia, throughout Africa, and in northern Australia. It can thrive even in desert climates and poor soil.

Here is a photo of the plant showing the characteristic leaf pattern and small yellow flower.

Like many weedy species, this plant has many common names. Puncture Vine, Caltrop, Yellow Vine, and Goathead are the most widely used; others include automobile-weed, bindy eye, bindii, bullhead, burnut, burra gokhroo, calthrops, cat's head, common dubbeltjie, devil's thorn, devil's weed, doublegee, dubbeltje, gokshura, ground bur-nut, isiHoho, land caltrop, Maltese cross, Mexican sandbur, puncture weed, rose, small caltrops, sticker, tackweed, and Texas sandbur (also T. micrococcus).

It is a taprooted herbaceous perennial plant that grows as a summer annual in colder climates. The stems radiate from the crown to a diameter of about 10 cm to over 1 m, often branching. They are usually prostrate, forming flat patches, though they may grow more upwards in shade or among taller plants. The leaves are pinnately compound with leaflets less than a quarter-inch long. The flowers are 4–10 mm wide, with five lemon-yellow petals (see above).


A week after each flower blooms, it is followed by a fruit that easily falls apart into four or five single-seeded nutlets. The nutlets or "seeds" are hard and bear two to three sharp spines, 10 mm long and 4–6 mm broad point-to-point. These nutlets strikingly resemble goats' or bulls' heads; the "horns" are sharp enough to puncture bicycle tires and to cause painful injury to bare feet.

Locally, the plants grow in vacant lots, along roadways, and on sidewalks. Here is a plant just down the street from our home in Kennewick, WA.

See how it grows in the crack between the asphalt of the parking lot and the sidewalk. It has a taproot, which means it has a long, single root that reaches way down into the ground and does not need a lot of room. It lies very flat to the ground and branches out with long runners.




The fruit or nutlets are quite fierce on these plants. Large and scary. The pictures here are of thorns that are still "green" and not hard enough to do any damage yet. But, they will dry out and then they will be able to stick into shoes, tires, etc.















Goathead Industry

Kennewick is known for Red Wine and Goatheads and both are quite important to the local economy. Goatheads are exported to various foreign governments for use as anti-personnel weapons. Long thought to have been native plants, they are actually invasive plants genetically engineered by the US Dept. of Homeland Security as our first line of defense against Canadian cyclists. We understand that one of the purposes of the Sea to Sea tour was to test out this system; fortunately it demonstrated that it does not work. In the fall goatheads are harvested laboriously by hand and turned into edible breakfast cereal. The sharp thorns are removed and the goathead "heart" is roasted and sold as Grapenuts Cereal.