Tumbleweeds are an iconic symbol of the old west.
It’s hard to imagine the american desert without a rolling piece of dry vegetation,
but most of the tumbleweeds you’ve seen are actually native to the great steppe of the
Ural mountains in Russia. Making them historically more tied to Ghengis Khan than American Cowboys.
Hi I’m Tasha the Amazon and you’re watching Floralogic.
The famous tumbleweed you’ve seen in the movies is Kali Tragus, AKA, the Russian thistle or salsola.
As their name suggests it’s an European plant,
whose seeds were accidentally introduced to North America in packages of flaxseed seeds.
For most of its life kali tragus looks nothing like a wicker beach ball.
It starts off as a soft herb. It’s tender enough that some people put them in their power salads.
But as it gets bigger it gets woodier, pricklier, and round. At that point it’s too hard to eat
even for deer and other large mammals. Small rodents use it for shelter, as the thorns turn
it into an impenetrable fortress. Kali Tragus is an annual herb,
so soon after it flowers it starts to die. Their death gets the ball rolling.
After it dies the roots break off and the plant separates from the floor.
By the time they’re fully grown they can be huge.
Some can be over 10 meters in diameter. And yet, they’re light enough that a
good gust of wind can push it around for miles. This is the most important moment of their lives.
As they tumble around they drop their seeds along its path.
A lot of plants use animals to disperse their seeds. Tropical fruits rely on monkeys and other
mammals to take the fruits and drop the seeds elsewhere, for example. And avocados originally
evolved to be eaten and have their seeds disseminated by the now-extinct giant sloths.
But the tumbleweed is a strong independent plant that needs no sloth.
It just uses the power of the wind. As it rolls, up to 200,000 seeds can be dropped
by a single plant. And those who land in moist areas will have the best chance of survival.
This strategy has helped them conquer most of the US and southern Canada.
It’s worked a little too well though, and they’re now considered an invasive species.
Multiple tumbleweeds can accumulate and create traffic jams, block houses, and damage cars as
they roll through towns. But the main reason they’re so dangerous is that they’re very
flammable. They have very high nitrate levels that turn them into wandering fire hazards.
Efforts to control it have been futile, as they reproduce quickly,
prolifically, and over vast distances.
But kali tragus is not all bad. They’ve been a reliable source of food in times of scarcity.
During the dust bowl they were the only source of food for millions of livestock in the US.
And then there are other tumbleweeds that are not as destructive.
The term tumbleweed generally refers to kali tragus, but it can more broadly refer to any
plant that disperses its seed in the same way. The plains tumbleweed is a native north american
plant that produces delicious edible seeds and don’t get quite as big as the kali tragus.
The tumbling saltbush of Europe and Asia also rolls around at the end of its life,
but it has smoother leaves. It gets to be around 1.5 meters tall.
In the tropics of the Americas, the white amaranth or white pigweed makes
tiny little tumbleweeds of about 50 cm. It has successfully been introduced to
every other continent except Antarctica. Its cousins, the mediterranean amaranth and
the red-root amaranth, are probably the most delicious tumbleweeds.
Their leaves are great in stews. And lastly, the highly invasive diffuse knapweed,
which can take over grasslands and harm animals’ throats with its prickles.
If you’ve ever been in the wilderness in Nrth America, you’re very likely to have seen one.
These guys are immensely successful plants. Sometimes they affect human populations,
but there’s little we can do about them. They might be dangerous, but that’s how they roll.
Ah my car! Holy smokes.
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