Not all thistles are noxious
Mountain Life
This last weekend, I hiked with my husband up Arapahoe Pass. It is a beautiful year for wildflowers. Columbines, sky pilot, paintbrush, and avalanche lilies were out in profusion. Mixed in with these flowers was a prickly native thistle called Cirsium scopulorum, or mountain thistle. It’s a strange and interesting plant, and well-adapted to the harsh conditions of timberline.
As we hiked a bit further, I saw that some well-intentioned person had been pulling these thistles. I know this person had learned that many thistles are noxious weeds, crowding out our beautiful wildflowers – they must have thought they were protecting the spectacular display. However, in this case the thistle is one of the wildflowers! It may sound a bit counter-intuitive, but it is true.
Even though our native thistles are just as prickly – or in some cases, even pricklier—as the alien noxious thistles, they do play a valuable role in our ecosystem. The butterflies and bees enjoy the nectar, and songbirds relish the seeds. So, please leave the native thistles to grow, while at the same time working to eradicate the Eurasian bullies.
How do you tell the difference between the natives and the noxious thistles? In mountainous Boulder and Gilpin Counties, it’s not too hard. It’s easiest to learn how to recognize the noxious thistles, since we have only two common ones – Musk and Canada. Both have purple flowers. Musk thistles have large flowers with a fearsome set of bracts just below the flowers; each flower is borne singly on the stalk. They can grow anywhere from waist-high to over your head. Canada thistles spread by creeping rhizomes, and can form dense, large stands. They have relatively small flowers, and they are borne in clusters on the stalks. They grow 2- 3 feet tall. Occasionally, one of the other noxious thistles from the flatlands (such as Bull, Scotch, or Plumeless) finds its way up here, but it’s very unusual, so we concentrate on learning to recognize the common two villains.
Our native thistles, in contrast, tend to have creamy white, light pink, or brownish flowers. They grow fairly sparsely, and never spread by creeping roots. The underside of the leaf is usually white or very light-colored. If you are above timberline, all of the thistles you see will be our native thistles. Visit the Gilpin Extension website to see more pictures of our native thistles: www.extension.colostate.edu/gilpin/nativethistles.shtml.
Irene Shonle is the Director of CSU Extension in Gilpin County. The CSU Gilpin County Extension Office is located at the Exhibit Barn, 230 Norton Drive, Black Hawk, CO 80422, 303-582-9106, www.extension.colostate.edu/gilpin.
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