This is musk thistle (Carduus nutans) also known as nodding thistle. It is a common weed in my area and a curse to farmers who find it hard to eradicate. We have quite a few plants growing on our property which I don't really mind as the honey and native bees love it. The leaves and seeds are used as a bitter tonic to stimulate liver function and it's also used as a wild food by peeling the rind from the stalks while they are still fleshy and succulent.
Proprietor, author, and tutor of The Home Herbalist Online Course.