Most people regard all thistles as invasive weeds. I happen to think they are beautiful and I have taken photos of them all over the world.
Recently we had a thistle sprout in the driveway. I decided to let it grow. Several species of thistle are native to Southern California and their nodding flower heads provide seed for our local lesser goldfinches and house finches. The down that creates the parachute to help spread the seed is used by a variety of birds and small creatures to provide plush comfort to their nests and homes.
The thistle in the drive has flowered and I think it is lovely–prickly, but delicate.
However, after consulting a few books and two reliable websites Oregon State University and Invasive.org, I have identified my thistle as a bull thistle (Cirsium vulgare) a European / western Asian import. The “vulgare” in its scientific name means common. This imported thistle can be highly invasive and problematic.
For the sake of my local wild environment, this thistle must go.
Some “weeds” are welcome additions to your backyard biodiversity, others are not. If you have a thistle find out if it is a beneficial native or a problematic invasive and act from a position of knowledge.