How to Identify Puncture Vine (a.k.a. the Goathead Monster)

This post originally appeared on Idaho Botanical Garden’s blog. With the first annual Boise Goathead Fest fast approaching, the purpose of this post is to help people in the Treasure Valley identify goatheads so that they can collect them for drink tokens to use at the event. I’m reposting it here in hopes that people around the globe who are tormented by goatheads might benefit from it. All photos in this post were taken by Anna Lindquist.

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If you have spent much time on a bicycle in Boise, chances are you have been the victim of a goathead-induced flat tire. You probably even got a good look at the spiky nutlet as you went to remove it from your tire. But where did the culprit come from? No doubt, it came from a plant. But which one?

This is particularly useful to know right now because the first annual Boise Goathead Fest is coming up, and if you manage to fill a garbage bag full of these noxious weeds before the end of July, you will earn yourself a drink token. Fortunately, this plant is fairly easy to identify; however, there are a few look-a-likes, so it is important to familiarize yourself with the plant in question so you can be sure you are pulling the right one.

puncture vine (Tribulus terrestris)

Puncture vine, also known as goathead or Tribulus terrestris, is a warm season annual that is native to the Mediterranean region of southern Europe. It was introduced to North America unintentionally by early European settlers when the plant’s blasted burs snuck their way across the ocean in sheep wool. Since then, puncture vine has spread across the continent prolifically thanks to the hitchhiking prowess of its seeds.

Behold, the infamous Goathead Monster.

Puncture vine has a prostrate habit, meaning that its branches lie flat on the ground, spreading outward from a central location. It grows upward only when it is being shaded or crowded out. Its leaves are divided into several tiny leaflets, and its flowers are small and bright yellow with five petals. It is an otherwise pretty plant were it not for the threatening, jagged fruits that follow the flowers. As these fruits dry, they dislodge from the plant, split into five pieces, and lay in wait to puncture your tire, work their way into the bottom of your shoe or the foot of an animal, or latch onto some errant fur.

puncture vine (Tribulus terrestris)

Depending on the conditions, puncture vine either remains fairly small or spreads as much as six feet wide. Fruits start forming shortly after flowering, and seeds ripen soon after that, so if the plant isn’t removed quickly – nutlets and all – future populations are guaranteed. Luckily the plants are fairly easy to remove. Unless the ground is particularly compact, they pull up easily, and if they break off at the root, they generally don’t sprout back.

Virtually any plant that has a prostrate growth habit and is actively growing in the summer could, at first glance, be mistaken for puncture vine. Closer inspection will help confirm the plant’s true identity. Two plants that might confuse you are purslane and spotted spurge. Both of these species can be found growing in full sun in disturbed or neglected sites in close company with puncture vine.

Purslane has tiny, yellow, five-petaled flowers similar to puncture vine; however, its leaves are glossy and succulent-like and its stems and leaves often have a red to purple hue to them. Purslane seeds are miniscule, and while the plant can be a nuisance in a garden bed, it poses no threat to bicycles or wildlife.

purslane (Portulaca oleracea)

Spotted spurge, also known as prostrate spurge, can be quickly distinguished by the milky sap that oozes from its broken stems. Its leaves are generally reddish purple on the undersides with a purple spot on top. Its flowers are minute and its seeds even smaller. Because its sap contains latex and other chemicals, it can irritate the skin and poison creatures that dare eat it.

spotted spurge (Euphorbia maculata)

Both of these plants are introduced, weedy species, so even if they won’t count towards your drink token, it still doesn’t hurt to pull them. Puncture vine, however, is included on Idaho’s noxious weed list, which means it is particularly problematic. So take this opportunity to pull as many as you can, and hopefully we can put a sizeable dent in the population of a plant that has tormented Boise bicyclists for far too long.

See Also: Plant vs. Bike

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Plant vs. Bike

Summer is drawing to a close in the northern hemisphere. Days are getting shorter. Nights are getting cooler. Fall flowers are beginning to bloom. And bicycles are getting more flat tires.

As an avid bicyclist, I am particularly aware of the waning summer season, especially since I live in a region where Tribulus terrestris is a prevalent weed. Commonly known as puncturevine or goathead, this nuisance plant is the bane of many cyclists’ existence. While the plant itself appears innocent, its fruit is quite the opposite. Rough around the edges and bearing large, rigid spines, puncturevine fruits easily penetrate bike tires, causing flats. They can also result in an uncomfortable experience for the bare-footed.

Native to the Mediterranean region, puncturevine made its way to North America sometime during the European immigration and has since spread across the continent. The fruit of puncturevine is called a bur. Plants with this type of fruit are benefited in two main ways: herbivory deterrent and seed dispersal. The spinyness of the burs deters insects and animals from eating their seeds, and the spines of the burs attach to the feet and fur of animals, etc., aiding in the dispersal of their seeds.

In cool climates, puncturevine is a summer annual. It appears in the heat of the summer, and by late summer the plants have mostly died off, leaving behind hordes of burs, awaiting the arrival of unsuspecting animals, bike tires, and otherwise. The spines of the burs attach themselves to these unsuspecting vicitims and are spread far and wide. The plants typically grow prostrate but can grow upright when they are in shade or being crowded out. They produce large mats that can spread as wide as 6 feet. Their leaves are oppositely oriented and are pinnately compound. Their flowers are small with five bright yellow petals that appear singularly in the axils of leaves. Their fruits are burs that split into 4-5 sections, each containing 1-2 large spines. Their seeds can remain viable for up to 20 years. Puncturevine is a fast growing, drought-tolerant plant with a long, slender taproot. It is commonly found in disturbed sites, along roadways and walkways, and in pastures and fields.

While I am fascinated by this plant, I also abhor it, and so I make an effort to remove and kill it whenever possible. If it weren’t for the countless flat tires it has caused me, I’d probably be more willing to let it be. Bike enthusiasts who have experienced this nuisance nod in agreement.

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Tribulus terrestris looking sweet and innocent

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Close-ups of pretty flowers, interesting leaves, and evil burs

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Bur of puncturevine puncturing bike tire