The results strongly contradict predictions in earlier studies that Salsola ryanii would not likely become invasive.

Salsola ryanii is an allopolyploid, an organism with two or more complete sets of chromosomes derived from different species, formed via hybridization between two other invasive tumbleweed species: Salsola tragus and Salsola australis. (Allopolyploids are not rare among plants. For example, wheat and cotton are also allopolyploids.)

Salsola australis is invasive in California and Arizona and is likely native to Australia or South Africa. It was not recognized as a distinct species until 2000.

Salsola tragus is a problematic weed in 48 states, according to the U.S. Department of Agriculture, and has been described as having the most rapid spread of any introduced species. Its native range extends from north Africa and western Russia, through Asia into northeast Siberia and northeast China.

The three species of tumbleweed are not distinguishable to the average person, said Welles, who earned her Ph.D. from UC Riverside in 2015. She used DNA testing to determine the species of the samples she collected.

The researchers believe the population expansion of the Salsola ryanii species is due to two reasons: dispersal of seeds from individual plants due in large part to the “tumbling” phenomenon and multiple independent hybridizations of the two original tumbleweed species. Future research will further examine this issue.

The research was funded by grants from the National Science Foundation.