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.
Tribulus terrestris looking sweet and innocent
Close-ups of pretty flowers, interesting leaves, and evil burs
Bur of puncturevine puncturing bike tire
awkward botany 