Trifolium fucatum is a species of clover known by the common names bull clover and sour clover. It is native to California and Oregon, where it grows in many types of habitat, becoming common to abundant in some areas. Trifolium fucatum is an annual herb growing decumbent to erect in form, the stem often thick-walled and hollow. The leaf blades are made up of oval or rounded leaflets with smooth or toothed edges, and the leaves have large stipules. The inflorescence is a head of flowers with a base of wide bracts. Each flower corolla is 1 to 2 centimeters long and white or yellowish with purple tips. The flower becomes inflated as the fruit develops.