The Pistachio (Pistacia vera, Anacardiaceae; sometimes placed in Pistaciaceae) is a small tree up to 10 m tall, native to mountainous regions of central and southwestern Asia such as the Kopet Dag mountains of Turkmenistan southwest to northeastern Iran and western Afghanistan. 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.

History
Pistachio is often confused with some of the other nine species in the genus Pistacia, such as P. terebithus and P. lentiscus. These species have a very different distribution, in the Mediterranean and southwest Asia, and have much smaller nuts, lacking the hard shell of P. vera. Their turpentine-flavoured nuts were a popular food in antiquity. Finds of Pistacia from pre-classical archaeological sites, or references in pre-classical texts, always refer to one of these other species (often P. terebinthus).

Pistachio (in the sense of P. vera) was presumably first cultivated in Central Asia. It reached the Mediterranean world by way of central Iran, where it has long been an important crop. Although known to the Romans, the pistachio nut appears not to have reached the Mediterranean or most of the Near East in any quantity before medieval times. More recently pistachio has been cultivated in California (first commercial harvest in 1976) 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.

Cultivation and uses

The kernels are eaten whole, either fresh or roasted and salted, and are also used in ice cream and confections such as baklava.

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). Roasted pistachio nuts turn naturally red if they are marinated before in a salt and strawberry marinade, or salt and citrus salts

The trees are planted in orchards, and take approximately seven to ten years to reach significant production. Production is alternate bearing or biennial bearing, meaning the harvest is heavier in alternate years. Peak production is reached at approximately 20 years. Trees are usually pruned to size to make the harvest easier. One male tree produces enough pollen for eight to twelve nut-bearing females. Pistachio orchards can be damaged by the fungal disease Botryosphaeria panicle and shoot blight, which kills the flowers and young shoots.

Pistachio nuts are highly flammable when stored in large quantities, and are prone to self heating and spontaneous combustion (see Cargo container's handbook).

California produces almost all U.S. pistachios, and about half of this is exported, mainly to China, Hong Kong, Japan, Europe and Canada. Almost all California pistachios are of the cultivar ' Kerman'. The tree is grafted to a rootstock when the rootstock is one year old.

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