What a pretty little yellow flower! It’s called Common Goldstar and the scientific name is Hypoxis hirsuta. “Hirsuta” means hairy and you can see little hairs on the buds of this specimen. According to Missouri Plants, the amount of hair on the plant can be quite variable. I didn’t see a lot of these, but reference suggest it is quite common and can even invade lawns. The flowers are about an inch across and the leaves are grass-like.