Yes, it is true, Colorado is home to five invasive-not-so-welcome-thistles. The invasive thistles can be extremely hard on native plant communities. In Boulder County, Colorado, the invasive thistle species of concern include Bull Thistle, Musk Thistle, Canada Thistle, Scotch Thistle, and Plumeless Thistle. These species are considered noxious weeds due to their ability to outcompete native plants, reduce biodiversity, and potentially impact livestock grazing. 

If you have thistles on your property and they are left to proliferate, they can spread throughout the community

Here's a more detailed look at each:

Bull Thistle (Cirsium vulgare):

Musk Thistle (Carduus nutans):

Canada Thistle (Cirsium arvense):

Scotch Thistle (Onopordum acanthium):

Plumeless Thistle (Carduus acanthoides):

Please, remove thistles from your property to curb the spread of these invasive species.  Over the years, they have spread throughout the properties in the Bar-K and on the Association land.  There are many folks in the community that have taken it on as a task to remove them.  Please help them by ensuring that the thistles on your own property are not allowed to spread.  Thank you!!