http://www.straightdope.com/mailbag/mtumbleweed.html
It seemed to me that the response on the Tumbleweed question came from someone who has never been west of the Mississippi. The tumbleweeds we have out west are not native to the Americas, but in fact, come from the Russian Steppes (indeed, some westerner intellectuals refer to the weed as Russian Thistle). They are, indeed, a major annoyance. They grow anywhere a weed will grow, and to enormous size, if allowed. When they dry up, they blow away (actually tumble along) and can collect in huge piles. They are also highly flammable (great fun to burn for us kids back in the pre-ecology days). Did I mention that they are covered with prickly spines?
I have spent many years West of the Mississippi, and live in California right now. I gave an honest answer - there are many plants CALLED “tumbleweed” by the Average Joe, but only one - Amaranthus albus - is given that as an official name. You’re referring to Salsola kali, which, along with other Salsola species, has a similar habit of tumbling, but is not the same plant at all (nor is it a thistle); it’s A tumbleweed, not THE tumbleweed. I know the plant well. I guess the critical thing may actually be which plant is seen rolling along in all those western movies - and it happens to be A. albus.
Tumbling pigweed, right? Wasn’t it introduced from the tropics? I didn’t think it was actually native, though it’s not from Russia like the one the OP was referring to. I saw a picture of pigweed, and it didn’t look exactly like what we in New Mexico refer to as “tumbleweed,” either. Any idea what ours is, Doug?
Jill asked: “Tumbling pigweed, right? Wasn’t it introduced from the tropics? I didn’t think it was actually native, though it’s not from Russia like the one the OP was referring to. I saw a picture of pigweed, and it didn’t look exactly like what we in New Mexico refer to as “tumbleweed,” either. Any idea what ours is, Doug?”
Ours is that tropical “tumbling pigweed”, though it doesn’t look much like other species of pigweed. It’s apparently been here a lot longer than the Russian Thistle, too (I also discovered that plant was recently reclassified as Salsola tragus, instead of S. kali).