YouTube Videos B2: Why Do Tumbleweeds Tumble?

They're prickly.

Restless.

Rambling.

But if most plants are perfectly content to stay in one place,

why does the tumbleweed hit the open road?

Tumbleweeds start out as tiny seedlings.

They sprout in late winter.

By summer the plant takes on its round shape.

They grow flowers nestled between thorny leaves.

Inside each flower, a fruit with a single seed develops.

This fruit is different than something delicious like cherries.

Lucky for the cherry tree, a bird will carry the fruit away in its belly and disperse its seeds.

But the tumbleweed takes matters into its own hands.

Come fall, the plant dries out and dies.

The seeds are still in there.

Gusts of wind easily break the dead tumbleweed from its roots.

See where it was attached?

It looks kind of like bones.

A special layer of cells at the base of the plant makes this clean break possible.

Then the skeleton is off, shaking loose tens of thousands of seeds as it goes.

It turns out, some living things spread their seeds better when they're dead.

Like cowboys in a Western, tumbleweeds head out on the open range.

But these icons of the American West actually come from the east, all the way from Ukraine.

They're a common weed in Russia too. That's why they're called Russian thistle.

They might have hitched a ride here in the 1800s hidden among flax seeds.

Nowadays, they might amble onto the freeway and make you swerve.

Or get tangled up in your irrigation system.

They could even roll into your neighborhood, pile up and become a fire hazard.

But a green lawn isn't what the tumbleweed is looking for.

It can't compete with plants like grass.

It needs a barren place like this abandoned onion field north of Los Angeles.

With each bounce the tumbleweed sends its seeds flying.

It spreads them out so they all get plenty of sunlight and space.

The coiled-up embryo inside just needs a little water to sprout.

And soon enough, this plant will strike out on its own.