Horse nettle, Solanum carolinense, is starting to pop up its thorny heads in the not-recently-cultivated plot beside our garden. It is growing fast and every surface (save the flowers) seems to be covered in sharp thorns. Even the roots have thorns!
It is in the nightshade family. While native, it is invasive. When I first noticed it, I deliberately stepped on each of the several plants that were close to our border. The following day, after a rain, they looked as vigorous as ever and were even blooming. That was when I took these photos.
So after the photo session, I used loppers to cut each to the ground. I am sure that will not kill them, but it will slow them a little and it at least kept the flowers from going to seed.