The Pistachio (Pistacia vera, Anacardiaceae; sometimes placed in Pistaciaceae) is a small tree to 10 m tall, native to southwestern Asia (Iran west to the Levant). It has deciduous pinnate leaves 10-20 cm long.

The plants are dioecious, with separate male and female trees. The flowers are apetalous and unisexual, and borne in panicles. The fruit is a drupe, containing an elongated seed (a nut in the culinary sense, but not a true botanical nut) with a hard, whitish shell and a striking light green kernel, having a very characteristic flavour.

When the fruit ripens, the shells split open partially (see photo). This happens with an audible pop, and legend has it that lovers who stand under a pistachio tree at night and hear the nuts popping open will have good luck.

Cultivation and uses

Pistachio nuts in the shell and out of it

Pistachio nuts have been a part of the human diet at least since the late paleolithic. The kernels are eaten whole, either fresh or roasted and salted, and are also used in ice cream and confections such as baklava.

One of the best places where it grows in abundance has historically been central parts of Iran. From there, it has been introduced in cultivation to the rest of the Mediterranean region by Roman times or earlier, and more recently to California and Australia. The word pistachio itself is perhaps a Middle Persian loanword into English and may be a cognate to the Modern Persian word پسته Pesteh.

The shell of the pistachio is naturally a beige colour, but it is sometimes dyed red in commercial pistachios. Originally the red dye was applied by importers to hide stains on the shells caused when the nuts were picked by hand. However most pistachios are now picked by machine and the shells remain unstained, making dyeing unnecessary (except that some consumers have been led to expect red pistachios).

The trees are planted in orchards, and are usually pruned to size to make the harvest easier. One male can pollinate about 12 nut-bearing females. Pistachio orchards can be damaged by the fungal disease Botryosphaeria panicle and shoot blight, which kills the flowers and young shoots.