“Monster tumbleweed,” scientists at UC Riverside call it, like a character out of a bad midnight movie.
But the invasive weed is a real thing, growing, expanding – and not ready to ride off to the sunset, a new University of California, Riverside study shows.
Long a movie-set stand-in for desert desolation, tumbleweeds are far from dusty ghost town relics. This species specifically. It’s called Salsola ryanii and it’s massive - much larger than its parents’ top height of 6 feet, the Riverside scientists say.
And the reason why, the study’s authors theorize, lies in the building blocks the plants’ Mom and Dad passed down: chromosomes, lots of them.
Four sets, in fact. Two from the plant’s mother. Two more from the father. Scientists label this “polyploidy” – hybrids with more than two sets of chromosomes. Humans, by comparison have two sets: one each from the mother and father.
“Salsola ryanii is a nasty species replacing other nasty species of tumbleweed in the U.S.,” said study co-author Norman Ellstrand, UC Riverside Distinguished Professor of Genetics, in a university story last week on the scientist’s findings. Ellstrand wrote the study with Shana Welles, Ellstrand’s laboratory assistant, whose research was part of her doctoral study. “It’s healthier than earlier versions, and now we know why.”
Ellstrand and Welles’ findings were published last month in the Oxford University journal AoB Plants.
The combination of multiple sets of chromosomes produces a bouncing baby hybrid. And a more thriving one. The plants grow more aggressively than their forebears, according to the study.
That’s potentially bad news for those who live near the notoriously invasive species, which is just about everywhere. Tumbleweed is almost universally invasive in the U.S., believed to be so in 48 states.
Tumbleweed can swarm farmland, are driver safety hazards when blown across roadways, are highly combustible and can bury homes.
Wells told UC Riverside that Salsola ryanii’s footprint is still a small one, but is spreading rapidly. Because tumbleweed grows in the late winter months, climate change could accelerate its spread, Wells said.
“It’s one of the only things that’s still green in late summer,” Welles said. “They may be well positioned to take advantage of summer rains if climate changes make those more prevalent.”