Tumbleweed Connection: New Species Spreads In California

Research from UC Riverside has found a new tumbleweed species (Salsola ryanii) has literally taken off since it was first identified in 2002 by scientists from the California Department of Food and Agriculture.

"This new species formed via hybridization in the Central Valley of California," says Shana Welles, who did the tumbleweed research as a graduate student at UC Riverside, where she earned her Ph.D. in 2015. 

She says the new species is an allopolyploid, an organism with two or more chromosome sets derived from two other different invasive tumbleweed species.

"They're very, very large," says Welles, now doing post-doctoral work at the University of Arizona. "They can grow up to six-feet tall, and the way they disperse their seeds is by breaking off at the base of the plant, once they have matured, and then dispersing their seeds using this tumbling mechanism." 

And, those tumbling plants are also hazards on state highways.    

As it turns out, Welles says humans have a hand in the spread of these tumbleweeds.

"They grow in very disturbed areas, and do a very good job of exploiting niches that have been opened by people," Welles says. "Roadsides and the sides of agricultural fields are places that they often grow, so they can be a pest to farmers and ranchers in that way." 

Welles did the field work in 2012, collecting tumbleweed from 53 sites in California.

She says the new species was found at 15 of those locations, including coastal areas around San Francisco and Ventura.

Her paper on the new species was recently published in the American Journal of Botany. 

The paper, "Rapid range expansion of a newly formed allopolyploid weed in the genus Salsola," was co-authored by her Ph.D. advisor, Norman C. Ellstrand, a professor of genetics at UC Riverside.