Russian Thistle
Salsola kali
This plant is the tumbleweed that
blows across the movie screen in old westerns. In real life, tumbleweed
is one of the worst hay fever culprits in the West, where the plant
grows abundantly. Tumbleweed pollen is formed in flowers so tiny
they are hard to see in the plant's tangle of branches. If you look
closely, you'll find them growing in the angles where the leaf and
stem meet. The male flowers make lots of tiny pollen, and the plant
depends on the wind to spread the pollen to other tumbleweeds. How
Russian thistle turns into a tumbling weed is an interesting story
the movies don't tell. The process starts in spring when the young
plant grows into a thick bushy ball. After flowering and forming
seeds all summer, the plant dries up, breaks off at the root, and
blows away in the wind. As it rolls around, it scatters seeds far
and wide. When tumbleweed seeds came to the United States with settlers
from Russia, they took root on the central plains. The plants then
rolled up into Canada and down into Missouri. Soon they spread to
California and the Pacific Northwest. Now Russian thistle grows
just about everywhere on the continent, though it still grows best
in the West.
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