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Last weekend I went to the Celtic Festival, which was also called the Highland Games, up at Floyd Lamb State Park. A wild Scottish event, with people tossing cabers (they looked like telephone poles to me), and flinging sacks of barley over high bars, and tossing heavy iron balls attached to chains. And terrific music, especially if you like bagpipe bands. Very entertaining - it really was fun.

One thing you notice when you spend time around people and things that are Scottish is the symbol of the thistle. You find it on all manner of decorations.

Thistles are so interesting. Once upon a time I worked with a guy who told me that he'd set up a whole thistle garden at UC Riverside a few years before. I thought he was really odd, because I used to think of these plants exclusively as weeds.

Heaven knows we use the term "thistle" pretty commonly, to describe many plants with spiky leaves. They don't have to be real thistles at all for us to use the name. Take Russian thistle for example. It's certainly spiny enough, but tumbleweed's not a thistle at all. In fact, it's more closely related to sugar beets, or spinach, than it is to true thistles.

There's a bit of botanical nomenclature called the "tribe". I knew that there was an "orchid tribe", but I just found out that there's a "thistle tribe" as well (and probably tons of others that I'll be learning about). Now, yellow star thistle, a weed that's taken over much, much of California's grazing lands is a member of the tribe. We don't have that particular invader down here in the south yet, but a similar thistle-named weed - Malta star thistle - is already a big problem in northern Nevada. It has yellow flowers and spines, too. What a lot of us tend to think of as "true thistles" definitely have spiky leaves, but their flowers tend to be in the pinkish - to reddish - to purplish color palette. Except for perennial sow thistle, which also has yellow flowers, and is certainly a weed.

I don't want give anybody the mistaken impression that what I'm calling "real" thistles (for want of a better term) can't be problems. Some thistles with purplish and pinkish flowers are listed as noxious weeds (and that's a legal term) - there's Canada thistle, for instance, and another one called "Yellowspine thistle". Neither of them is problematic in Southern Nevada so far.

Scotch thistle, on the other hand, is on our Nevada noxious weed list, as is something called musk thistle. According to Dr. Wayne Johnson, who's the UNR state horticulture specialist, a rosette of musk thistle leaves can grow two feet in diameter during its first year; and in its second growing season, the plant can grow nine feet tall. I don't know about you, but the very idea of a nine foot tall, spiky leaved plant just fills me with dread. He also writes that scotch thistle, in its second year, can grow five feet wide and up to twelve feet tall. I don't even want to think about a spiny leaved plant that could be more than twice my height. There was a period of time when people would use scotch thistle for medicinal, and household purposes, but, those times are long past. We have fact sheets available at Cooperative Extension with information on controlling those weeds.

But not all thistles are problems, by any means. I know that I'd feel terrible if I couldn't have an occasional artichoke - it's been a luxury vegetable since Roman times. We have one species of true thistle that's only found in the Spring Mountains area, and it's listed as a "sensitive" species by the US Forest Service as well as the Nevada Natural Heritage Program. That means it needs to be protected, even though someone has described it as "the most savagely armed" member of its genus. It's called the Charleston Mountain thistle. There are other natives that we wouldn't want to see being harmed either - the Arizona thistle, the Mojave thistle and the Desert thistle. None of these is a short little shrinking violet; some of them can get as tall as seven or eight feet.

The point is that these plants have evolved in this area, as have lots of wild animals that ultimately feed on them. Something that has fiercely spiked leaves might be a noxious weed, but it might be plant that needs to be protected. So the lesson I'd like to get out today is, if you find a thistle with bluish, purplish or reddish flowers, think of Scottish bagpipe music, but call the cooperative extension weed specialist before pulling it.

For KNPR's Desert Bloom, this is Dr. Angela O'Callaghan of the University of Nevada Cooperative Extension.