Lycium is a genus of flowering plants in the nightshade family, Solanaceae. Lycium are shrubs, often thorny, growing 1 to 4 meters tall. The leaves are small, narrow, and fleshy, and are alternately arranged, sometimes in fascicles. Flowers are solitary or borne in clusters. The funnel-shaped or bell-shaped corolla is white, green, or purple in colour. The fruit is a two-chambered, usually fleshy and juicy berry which can be red, orange, yellow, or black. It may have few seeds or many. Most Lycium have fleshy, red berries with over 10 seeds, but a few American taxa have hard fruits with two seeds. While most Lycium are monoecious, producing bisexual flowers with functional male and female parts, some species are gynodioecious, with some individuals bearing bisexual flowers and some producing functionally female flowers.

Goji, goji berry or wolfberry is the fruit of Lycium barbarum and Lycium chinense, two closely related species of boxthorn in the Nightshade family, Solanaceae. The family also includes the potato, tomato, eggplant, deadly nightshade, chili pepper, and tobacco. The two species are native to Asia. Wolfberries are usually sold in open boxes and small packages in dried form. As a food, dried wolfberries are traditionally cooked before consumption. Dried wolfberries are often added to rice congee and almond jelly, as well as used in Chinese tonic soups, in combination with chicken or pork, vegetables, and other herbs such as wild yam, Astragalus membranaceus, Codonopsis pilosula, and licorice root. The berries are also boiled as a herbal tea, often along with chrysanthemum flowers and/or red jujubes, or with tea, and packaged teas are also available. Various wines containing wolfberries are also produced, including some that are a blend of grape wine and wolfberries. Young wolfberry shoots and leaves are also harvested commercially as a leaf vegetable.