Lycium (Solanaceae) is a hardy, drought-tolerant shrub that grows wild in and around the Tucson, Arizona, basin and other arid areas in U.S. Department of Agriculture plant hardiness zones 7 through 10. Characterized by thorny branches and red berries, it is often difficult to distinguish specific varieties. Though there are up to 15 types of Lycium that grow naturally in Tucson, they are generally referred to with the same common names: wolfberry, desert thorn and goji. Each variety excels in the arid, hot Tucson environment. They lose their leaves during the driest part of the year and decline to flower or fruit when water is scarce for extended periods. There are slight differences in the leaves and flowers that help distinguish one from another.
Wolfberry (Lycium berlandieri) grows 2 to 8 feet tall and wide, has barbed thorn branches, and smooth spatula or spoon-shaped leaves. This variety is also commonly called desert thorn and Berlandier wolfberry and it grows in USDA zones 7 to 9. The flowers are often white but small enough to often overlook. The plant has gray textured bark that provides interest in the garden when the leaves drop in the hottest months. The root system can expand 25 feet from the base however, and it suckers easily so it may not be the best Lycium to use in small landscapes.
Fremont's desert-thorn (Lycium fremontii) is a variety that can grow 3 to 9 feet tall and prefers USDA zones 9 to 10. It produces lavender and purple flowers that, while small, are larger and more noticeable than the flowers on other Lycium. The leaves are not quite as fleshy and smooth as the berlandieri. Some versions do not have thorns and those that do are not overly sharp. This combined with Fremont's tendency to grow in saline soils makes it a popular pick for growing in Tucson yards.
Arizona Desert-Thorn (Lycium exsertum) has tubular-shaped flowers that hang downwards. The leaves are spatula-shaped with fine hairs. It grows naturally in rocky, sloped locations in USDA zones 7 through 10.
Anderson's Desert-Thorn (Lycium andersonii) also has tubular flowers and barbed branch tips. The flowers are often a shade of purple but can sometimes be white tinged with purple. The leaves are fleshy and without hairs. This variety of Lycium likes to grow in and near sandy washes, also in USDA zones 7 through 10.