About 100, including:
Lycium afrum
Lycium barbarum - wolfberry
Lycium carolinianum
Lycium chilense
Lycium depressum
Lycium europaeum
Lycium ferocissimum
Lycium pallidum
Lycium ruthenicum
Lycium tetrandrum

Boxthorn (Lycium) is a genus of about 100 species of plants in the Solanaceae, native throughout most of the tropical and warm temperate zones of the world. Other names include Christmas berry, Matrimony vine, and the confusing "Tea-tree" (it is not related to tea, and with the foliage being toxic, should not be used as such).

They are shrubs, usually spiny, with deciduous or evergreen alternate, simple leaves 1-8 cm long. The flowers are solitary or in small clusters, 6-25 mm diameter, with a corolla of five purple, white or greenish-white petals joined together at their bases. The fruit is a red, purple or black berry 8-20 mm diameter, similar to a nightshade or bittersweet berry. In some species, notably L. barbarum (Wolfberry), the fruit is edible (see that species for further detail).