Lycium fremontii is a species of flowering plant in the nightshade family native to northwestern Mexico and the southernmost mountains and deserts of California and Arizona in the United States. It often grows in areas with alkaline soils, such as alkali flats, and is commonly known as Frmont's desert thorn. Both its common name, and its specific epithet are derived from John C. Frmont. L. fremontii is a bushy, spreading shrub approaching a maximum height of 4 meters with many thorny, leafy branches. The fleshy leaves are oval in shape and up to 2.5 centimeters long. Parts of the plant are coated in hairy hairs. The flower cluster is a small cluster of tubular flowers roughly 1 to 2 centimeters long including the cylindrical calyx of fleshy sepals at the base. The flower is light to deep purple with purple veining. The corolla is a narrow tube opening into usually five lobes. The fruit is a red berry 6 to 8 millimeters wide.