I found these flowers on the Causeway, which is a strip of land that crosses Mobile Bay. I'd never seen them before. It's called Carolina horsenettle (Solanum carolinense). The other names for this plant are not very kind--radical weed, sand brier, bull-nettle, tread softly, apple of Sodom, and Devil's tomato. It's apparently very painful to horses and humans should they run full long into it. One writing says that it continues to hurt for a very long time even after the thorn is removed.