The plant species salsola tragus is better known by its colloquial name: tumbleweed.
Tumbleweed first appeared in South Dakota in 1874. It was brought to the United States in flax seed from Russia, which is why scientists also call it Russian thistle. It’s considered an invasive species — the prickly, brambly orbs roll at random across open spaces, throwing off seeds as they go, which results in more and more tumbleweed.
Tumbleweed became a staple in Western movies — a symbol of the boom-and-bust cycle of life on the American frontier. For over a century, we thought we knew just about everything there was to know about it.
But then, in the mid-1990s, scientists Debra Ayres and Fred Ryan began gathering tumbleweed samples in Arizona and in California’s Central Valley. Ayres joined The Show to talk about how when they started testing the samples, they realized they weren’t just looking at Russian thistle.
Full conversation
DEBRA AYRES: We discovered that 40% of the plants that we sampled throughout the Central Valley in California were something completely different. This unknown tumbleweed that we hadn't hadn't identified anywhere in the world and it turned out it was this Australian tumbleweed.
So, somehow the Australian tumbleweed got into California and into Arizona. And we're not sure which came first because this species was never identified until Dr. Ryan and I did it through molecular biology.
SAM DINGMAN: Interesting. And so if I'm hearing you right, this Australian version of tumbleweed was sort of hiding in plain sight for, for decades?
AYRES: Absolutely. And even now, I think that people look at tumbleweed and they say, “Oh, that's just tumbleweed, you know, big deal. It's a big, widespread weed. It occurs in all 48 lower states and who cares to map it?” But, it turns out it's kind of fascinating when you do map it.
DINGMAN: Well, so before we get to, some of the other fascinating elements of it, tell us why tumbleweed tumbles. What, where does it, where does the name come from?
AYRES: Well, this is actually a fascinating dispersal mechanism. In Russian thistle, but maybe not so much in the Australian thistle, the bottom of the plant, the stem part where it meets the roots, it breaks off naturally. And when it breaks off, the plant is round, like a ball, the wind picks it up and blows it until it stops by a fence or a tree or a house.
There are some amazing pictures on the web, where the tumbleweeds are as high as the roof line and perhaps 20 deep, on houses where the wind has blown the plants and they fetched up against these houses. And then if the plants happen to catch on fire, there's big trouble because the plants when they blow are very dry, they're very flammable and they can skip and blow into other tumbleweeds and start fires. So it's, it's a matter of some concern that there are these abundant tumbleweed populations
DINGMAN: And there is also now a third type of tumbleweed, correct? The so-called, “monster tumbleweed.”
AYRES: Well, what happened was, Dr. Fred Ryan, he was in Coalinga and he noticed a tumbleweed that didn't look like either of the tumbleweeds we were familiar with, because we had identified both this mystery tumbleweed and then Russian tumbleweed. And, this was different than either one of them. And so, we did molecular biology and chromosome counts and all kinds of investigations on this mystery tumbleweed, and it turned out that the Australian and the Russian tumbleweed hybridized.
This new plant is a brand new species which was named after Fred Ryan, Salsola ryanii, Ryan's tumbleweed, and it's spreading and this new tumbleweed, Ryan's tumbleweed, is going to be more invasive than either of its parental species.
DINGMAN: And why is that? Is that because it, it's like larger and so it, has more flowers and, and therefore produces more, more seeds or?
AYRES: Exactly. The plant spreads, of course, by tumbling, and it latches onto cars, and it latches onto railroad cars. But, when the two species come together both the Russian and Ryan's tumbleweed can probably get almost as tall as a person. They're generally under 6-feet tall, and if they're globular, if they're like a ball, they're going to be 6-feet in diameter.
So that's, that can be a substantial plant. And, when it blows into the roadways, they break off and they blow into the roadways, it can be quite a challenge to, you know, drive up the Central Valley of California with these 6-foot diameter plants tumbling in front of you.
DINGMAN: Wow. So, let's talk a little bit about the iconography of the tumbleweed because the tumbleweed is, I think in the popular imagination, very much associated with the idea of the Old West kind of blowing through small towns. We've seen it a lot in westerns. But if I'm not mistaken, that is an anachronistic image?
AYRES: If we think that our Westerns occurred, you know, post Civil War sometime in the 1870s or something, tumbleweed wasn't here. Tumbleweeds just happened to tumble into Westerns that were made, you know, in the 1940s or '50s or something. So, they weren't, they weren't there, they weren't there in the 1870s.
DINGMAN: Why do you think, and you know, I realized I'd just be asking you to speculate here, but why do you think they became such an appealing image for filmmakers who were trying to tell the story of the Old West?
AYRES: That is such a great question. It could be that just happenstance. They're filming one of these, you know, dirt roads in the town and all of a sudden there's tumbleweeds tumbling in and, “What are we gonna do about these weeds tumbling in?” And they said, “Let's make it part of the movie.” I don't know.
DINGMAN: Necessity is the mother of invention, and all that. I have to say it is, you know, it's interesting to me, I was talking with our producer Sativa about this, and we're just kind of remarking on the fact that, you know, whether those filmmakers would have intended this or not, there is something quite metaphorical about the tumbleweed in terms of the nature of a lot of those stories, because it's this rootless, amorphous thing that is kind of carried west, spreading its seeds everywhere, sort of willy nilly, without regard for the damage that it might be doing. I mean, there is a sort of a manifest destiny, misguided American Dream connection there if you, if you want to find it.
AYRES: Probably not the only misguided manifest destiny in this country, but yeah.
DINGMAN: Is it correct to say that tumbleweeds are also, in a way, something of a harbinger of the effects of climate change?
AYRES: Not yet, no. But, the interesting question is, what will they do as climates become drier? Because they're very drought tolerant. If the moisture isn't there, how well do they survive? If they're able to access moisture that other plants can't because of the depth of their roots, I wouldn't bet against them.
You know, when they started spreading out of South Dakota, an agricultural commissioner, somewhere along the line, he said, “Kill it, now. If it appears in your landscape, kill it, kill it all.” And this was, you know, many, many, well, I don't know, 100 years ago maybe — “kill it all.” But that advice was not followed.
DINGMAN: Right, and here we are dealing with the monster tumbleweed.
AYRES: Yes, indeed.
