Pistachio nut (Pistacia vera), seed of the pistachio tree in the cashew family. Pistachio trees grow in western Asia, the Mediterranean, and southwestern U.S. The nut, which is about 1 in (2.5 cm) long, consists of a hard shell, smooth husk, and an edible green kernel. The kernel, which has a mild flavor, can be eaten whole. When ground, kernels are used to flavor foods; when pressed, they produce a cooking oil.