Here's a closer pic of the "flower buds."

That is a thistle - can't tell for sure if it is the Bull Thistle or one of the others. They are all quite similar. In some states you can be fined for having them on your property. Very destructive to cultivated farm land as well as pastures. Their seeds will spread for miles, and there are many, many seeds in each one of those flower heads. Please, get rid of it immediately. The roots are shallow and it is quite easy to take a shovel, drive down beside the plant and lift the plant out of the ground. Make sure you wear leather gloves, as those spines are very sharp and hard. Dispose of it in a garbage dumpster, not your compost pile.

In my yard across the country in Maine, they are a common thistle plant. A friend gave me one many years ago, when I was a beginning gardener, and I have rued that day ever since, with them popping up all over. I dig them up - very long root - whenever I can.

Here is a link that might be useful: Thistle

Thanks for the info!