The pistachio, technically known as “Pistacia vera,” is a small tree, growing up to 10 metres (33 feet) tall. It is a desert plant, originating from Central Asia and the Middle East, and is highly tolerant of saline soil.

The tree produces seeds – commonly known as “pistachio nuts” – that have been consumed as food for thousands of years. The kernels are often eaten whole, either fresh or roasted and salted, and are also used in pistachio ice cream, kulfi, spumoni, pistachio butter, pistachio paste and confections such as baklava, pistachio chocolate, pistachio halva, or pistachio lokum. Today about three quarters of the world's pistachios come from Iran and the United States.

The shell of the pistachio is naturally beige in colour, but it may be dyed red or green in commercial pistachios. Originally, dye was applied to hide stains on the shells caused when the nuts were picked by hand. In the 21st century, most pistachios are harvested by machine and the shells remain unstained.

“Pistacia vera” is often confused with other species in the genus “Pistacia” that are also known as pistachio. These other species have seeds which are much smaller and have a soft shell.

More Info: en.wikipedia.org