Picture in your mind a classic Old West showdown. Two gunslingers slowly advance towards each other down a deserted street, their spurs gently clinking with every step. They stop and stare each other down, hands hovering over the six-shooters slung from their hips. All goes still as the tension rises, the silence broken only by the whine of a harmonica or the hiss of a rattlesnake. A gust of wind blows across the street, throwing up a cloud of dust and sending a lone tumbleweed rolling between our antagonists. Then, in a flash, hands flash to belts, a gunshot rings out, and one man – the bad, guy, naturally – crumples to the ground.

Every detail of this scene has been burned into our collective consciousness by over a century of Western films, books, and television shows, interpreted and reinterpreted to the point of myth – or cliché. But while this archetypal scenario is mostly fiction – or happened far less often than pop culture would have us believe – at least one element is accurate: the tumbleweed. A visual staple of the Western genre, tumbleweeds poignantly evoke the desolation and ruggedness of the American frontier, and the lonely, drifting lifestyle of its mythical heroes. But what actually is a tumbleweed? Is it a specific plant, or just any dead bush rolling around in the wind? Where do they come from, and how did they come to be so emblematic of the American Old West? Well, pardner, put on your ten-gallon hat and chaps, saddle up, and let’s find out, shall we?

To answer the first question, tumbleweeds are not a single species of plant but many. Indeed, it is more accurate to think of tumbleweeds as a reproductive strategy rather than a specific type of plant. In botanical terms, a tumbleweed is a type of diaspore, a structure that helps a plant disperse its seeds. For example, the seeds of coconut palms spread by floating on water, the seeds of dandelion are scattered by the wind, while certain berries are eaten by animals and deposited far away in their droppings – which also furnish a convenient supply of fertilizer. Similarly, tumbleweeds allow plants to disperse their seeds by rolling in the wind. In some cases the entire plant above the roots forms the tumbleweed, while in others a hollow fruit or cluster of flowers breaks off and rolls away. In either case, once the plant has been fertilized and matured, the tumbleweed section dies off, leaving only a dry husk carrying a load of seeds. A special patch of cells called the abscission later then splits and the tumbleweed breaks free, allowing it to be carried away by the wind. In some species, the tumbleweed immediately starts shedding seeds as it rolls, while in others the hard casing around the seeds must be gradually worn down, ensuring that the seeds are dispersed sufficiently far from the parent plant. Given the need for wide open, windswept spaces with minimal obstacles for maximum dispersal, tumbleweeds largely grow in sparsely vegetated, arid or semi-arid environments.

Many different plant genera worldwide produce tumbleweeds, including Amaranthus in Central and South America, Ammocharis and Brunsvigia in southern Africa, Anastaticum or “Rose of Jerico” in North Africa, and the grasses Spinifex and Panicum – evocatively known as “hairy panic” – in Australia. Even non-seed-bearing plants and fungi can form tumbleweeds; for example, the moss Selaginella and the puffball fungus Bovista disperse their spores in this manner. However, the plant most of us are thinking about when we picture a tumbleweed is Salsola tragus, also known as “Russian Thistle” or “wind witch”. When first sprouting, Salsola looks fairly innocuous, with reddish-purple striped stems and thin, tender leaves which are commonly eaten by many animals, including mule deer, pronghorn, prairie dogs, and birds. As the plant matures, however, it grows into a woody, globe-shaped shrub covered in sharp thorns, which can grow up to the size of a Volkswagen Beetle. In the winter, the entire plant dies, dries out, and detaches from its root, forming the familiar tumbleweed we all know and love. Driven by the wind, these weeds can travel hundreds of kilometres, dispersing seeds as they go – around 250,000 per plant.

The seeds of Salsola are unusual in that they lack both a protective coat or endosperm – the stored energy reserves that gives most seeds a head start in germination and sprouting. Instead, they consist of a coiled, embryonic plant encased in a thin membrane. Consequently, Salsola seeds must wait until conditions are just right – around 20°C during the day and 5°C at night with adequate moisture – in order to sprout. They then quickly send up a pair of needle-like shoots, and the whole cycle begins anew.

But while Salsola has become inextricably linked with the American West, you may be surprised to learn that it is not actually native to that area. Indeed,  it is a relative newcomer to the Continent. And far from being a benign part of the landscape as many Westerns would have us believe, like most invasive species the tumbleweed has proven itself to be something of an ecological menace.

As its common name “Russian Thistle” suggests, Salsola is native to the steppes of Eurasia, and is thought to have arrived in North America in 1873. In that year, Russian immigrants arrived in Bon Homme County, South Dakota, carrying bags of flax seeds contaminated with Salsola. From there, the plant quickly spread across the continent. By 1877 tumbleweeds were a common sight in South Dakota, while by 1900 they had spread as far west as Bakersfield, California. As one government botanist sent to investigate the situation in the 1890s reported:

“One almost continuous area of about 35,000 square miles has become more or less covered with the Russian thistle in the comparatively brief period of twenty years.”

The plant’s ability to thrive in hot, dry environments and its high tolerance for salt already made it ideally suited to the American West, but it was the agricultural boom of the late 19th Century that truly made it spread like wildfire. Ordinarily, Salsola cannot compete with prairie grasses because grass seeds contain endosperm, allowing them to sprout earlier in the season. Thus, by the time conditions are right for Salsola to start sprouting, the surrounding grasses have already taken over. But the large ploughed fields and overgrazed pastures of the American frontier – plus the lack of natural predators or pathogens – provided an ideal, competition-free environment for Salsola to thrive and spread. The plant is now found in every U.S. state except Alaska and Florida, and has spread as far afield as Canada, Argentina, Norway, China, South Africa, Indonesia, and Japan.

But how, you may ask, can the humble tumbleweed possibly be a menace? Well, while a single tumbleweed might be fairly harmless, a whole bunch of tumbleweeds is a different story entirely. When trapped against fences and other obstacles, accumulations of tumbleweeds can form thick, barbed-wire-like masses that can block entire highways and completely bury vehicles and homes. In 1989, the town of Mobridge, South Dakota was overwhelmed by tens of tons of tumbleweeds which had blown in from the nearby Oahe dry lake bed. So deeply was the town buried that mechanical excavators had to be brought in to clear the prickly mess. A similar disaster befell Victorville, California in April 2018 and Hanford Reservation, Washington in December 2019. In the latter incident, which locals dubbed “Tumblegeddon”, tumbleweeds piled up to six metres high, completely burying houses and cars and closing Washington State Route 240 for ten hours straight. As State Trooper Chris Thorson recalled:

“Visibility was bad, which caused cars to slow down. When they stopped, the tumbleweeds were piling so fast, they just fully engulfed in minutes. It’s kind a strange mixture of weather and circumstances, I don’t know how to really explain it. It’s just odd. It’s so odd because it doesn’t happen. Typically, 99 percent of the time, you can drive through tumbleweeds.”

And this phenomenon isn’t unique to the United States. In 2016, the town of Wangaratta in Victoria, Australia was smothered under an avalanche of the tumbleweed grass Panicum effusum – also known as “hairy panic” – with some accumulations burying houses up to roof level. It took locals with leaf blowers weeks to clear the town, while the town council proposed attaching giant vacuum cleaners to street-sweeping trucks to tackle the problem. In addition to clogging roads and houses, such bone-dry tumbleweed accumulations also pose a significant fire hazard, with pileups on fences and other obstacles resulting in hundreds of wildfires across the United States every year. Even lone tumbleweeds can be hazardous; every year dozens of unsuspecting motorists encounter large tumbleweeds rolling across the highway and swerve to avoid them, often resulting in accidents.

Tumbleweeds also present a significant threat to agriculture and local biodiversity. By quickly colonizing unused land, tumbleweeds outcompete native species, while the wildfires they promote cause more land to be cleared, further accelerating the plants’ spread. In dry-land areas, they can also compete with crops for scarce water resources. Indeed, one study conducted by Washington State University in 2009 demonstrated that a single Salsola tragus plant can suck up to 167 litres of water from the soil in a single year – an volume that can easily make the difference between a good wheat crop and a bad one. By virtue of being one of the few plants in central California that stays green in the fall, Salsola is also a major host of the beet leaf hopper, the insect which transmits the curly top virus. This virus can damage a wide variety of crops such as sugar beets, tomatoes, melons, cucumbers, peppers, squash, spinach and beans, and pesticide spraying against the beet leaf hopper costs California farmers millions of dollars every year. And in the case of Australian “hairy panic”, overconsumption of this plant by sheep and other animals can cause a debilitating disease known as “Yellow Big Head.”

For nearly a century, common methods for combatting tumbleweeds – such as spraying herbicides, uprooting young plants, and removing mature tumbleweed accumulations with pitchforks – have proven crude, labour-intensive, and largely ineffective. In the 1970s, two species of moths were introduced to the United States in the hopes their caterpillars would keep tumbleweeds in check, but this, too, was ultimately unsuccessful. However, the situation is slowly starting to improve. In 2014, the U.S. Agricultural Research Service announced the discovery of two fungal pathogens native to Salsola’s original Eurasian home which might prove effective against the plant, while research is ongoing on the use of blister mites and weevils native to Tunisia and Kazakhstan.

There are also a variety of strategies farmers can use to curb the spread of tumbleweeds. For example, the government of the Canadian province of Saskatchewan recommends that cool-season crops like winter cereals and canola be planted as early as possible to pre-empt and outcompete Salsola seeds, which require warmer conditions to germinate. For farms growing less competitive crops like flax, lentils, and chickpeas, it is recommended that more competitive plants be added to the crop rotation in order to suppress overall Salsola seed production. Indeed, studies have demonstrated that while the germination rate of Salsola seeds can be high as 76% within the first year after shedding, due to the fragile nature of the seeds this drops off dramatically with time, falling to only 31% after one year, 0.5% after two years, and 0.04% after three years. This means that early and aggressive intervention against tumbleweeds – such as herbicide burnoff prior to crop seeding – can lead to their complete eradication in an area in only a few years. Fences or shelterbelts of trees, shrubs, and other plants around agricultural fields can also serve to block the wind and catch tumbleweeds, reducing the spread of their seeds.

But while the tumbleweed is widely condemned by farmers as a noxious weed, as Ralph Waldo Emerson once said: “What is a weed [but] a plant whose virtues have not yet been discovered.” Indeed, despite its reputation as a botanical menace, the tumbleweed is not entirely without its virtues. During the Dust Bowl of the 1930s, Salsola was one of the few edible plants that could survive in the depleted, desiccated soil of the American Midwest, providing a much-needed lifeline for cattle ranchers. In 1934, the state of Kansas alone produced over 350,000 tonnes of Salsola hay, the plant being widely credited with saving the cattle industry in the area. According to Timothy Egen’s 2006 book The Worst Hard Time, young Salsola shoots were also widely canned and eaten by people when all other food sources had run out.

And while responsible many kinds of of ecological disasters, tumbleweeds may actually help prevent others. One species of Russian Thistle, Salsola Kali, can absorb large amounts of toxic heavy metals like cadmium and technetium from the soil, meaning it could potentially be used to clean up contaminated sites. But whether burden or boon, one thing is for certain: the iconic tumbleweed is here to stay, and will continue to roll its way across the plains and deserts of the American West for centuries to come.

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