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Enormous Tumbleweeds Spotted In San Francisco For The First Time

A relatively recent hybrid has invaded much of California.

A good-sized Salsola ryanii, in the bed of researcher Shana Welles's truck. (Photo: UC Riverside)

A good-sized Salsola ryanii, in the bed of researcher Shana Welles’s truck. (Photo: UC Riverside)

Last fall, a tumbleweed made headlines when it took on a self-driving car and won.

What looked like a funny coincidence may have been a spiky scout. Researchers announced that a hybrid tumbleweed species, whose members can grow to the size of truck beds, has recently been spotted for the first time in San Francisco.

Despite their Old West reputation, all tumbleweeds are invasive—the group first came to the United States from Asia in the late 1800s, and has since buried towns, swamped farms, and interrupted technological progress all over the country.

This particular species, called Salsola ryanii, is a hybrid of two others: S. tragus and S. australis. All three species look mostly alike, but have different biological properties that affect how each interacts with the environment. Researchers first identified S. ryanii back in 2002, when it was mostly rolling around Central Valley and showed no signs of expanding its range.

Since then, though, it has ventured northwest to the San Francisco coast and south to Ventura. “We are not aware of any plant neospecies whose range spontaneously experienced such a dramatic expansion,” botanists Shana Welles and Norman Ellstrand wrote in their paper on the subject, recently published in the American Journal of Botany.

They fear this one may be heading out of California altogether. “This species has the potential to be a problematic invasive,” Welles told Phys.org. “We want to make sure people know that and try to manage this species when it still had a relatively narrow range.”

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