This rather scary plant (look at all those thorns!) is a type of wildflower that I first spotted a couple of years ago but never got around to identifying. When I saw it this year, it was late in the day, so this is not a good picture of the flowers. It does give a good idea of the plant’s overall appearance, though.
Seeing this plant’s flowers and leaf structure, I suspected that it was a nightshade. When I later saw its fruit, I was almost certain.
After researching this plant, I believe that it is horse nettle, which is indeed a nightshade. Horse nettle is not a very nice plant. Not only is it thorny, but it’s also poisonous. Horse nettle often ends up on lists of poisonous lookalikes because the fruit looks tomato-y (one of its common names “devil’s tomato”). Don’t let the fruit fool you. You do not want to eat any part of this plant, and neither does your horse, if you have one.