Silverleaf nightshade

This is a common weed/wildflower throughout Central Texas. Solanum elaeagnifolium Cav. (also called white horse nettle, trompillo, tomato weed, prairie berry, or bullnettle) is in the potato family.

While its purple flowers are pretty, according to the Lady Bird Johnson Wildflower Center, this is an aggressive, poisonous weed which spreads from very deep roots (6-10 ft). It grows in poor soil with very little water.
The poisonous yellow fruit, which remains on the plant for months, resembles tiny green-striped tomatoes and contains solasodine, a steroid compound used commercially to synthesize steroid hormones.

Medicinally, the root was used by shamans to treat rattlesnake bite - they chewed the root and then sucked on the wound to remove the venom, then additional root was chewed and applied to the swollen area. Pima Indians used the fruit as vegetable rennet to make cheese.