Plant 369

Pistacia vera L. (Anacardiaceae)


Pistacia vera produces the familiar pistachio nut. Today, the kernel is eaten out of the shell or used in confectionary such as baklava and Turkish delight, but archaeological evidence from Iraq and Turkey shows that the nut was used for food as early as 7000 BCE.

The tree’s native range is Central Asia to Afghanistan, from desert climates with hot dry summers and cold winters. Adapted to these arid conditions, it is regarded as a phreatophyte, a plant that has an extended root system that can reach the water table. As such, during periods of drought it will always have access to water and therefore does not need to store it, in contrast to succulent desert plants that have a less extensive root system but which store water and are termed xerophytes. The tree was introduced to Italy in the first century CE and spread to other Mediterranean countries; it was introduced to Australia and the United States in the nineteenth century.

Although drought tolerant, pistachio trees will produce an improved crop if well irrigated. They also require a long winter chilling period of 1,000 hours, which equates to a winter dormancy of about six weeks with temperatures below seven degree Celsius. Conversely, very hot summers are needed, with more than 600 hours over 30 degree Celsius, for the fruit to ripen.

Pistachios are small- to medium-sized, deciduous trees of 7-10 metres tall with pinnate leaves, each leaf axil has a single bud and most of the lateral buds develop into inflorescences. These fully develop the following year, thus bearing fruit on one-year-old wood. Trees will begin bearing after around five years but will not reach full production until after 15 to 20 years. They are dioecious, with both male and female plants bearing inflorescences of many hundreds of tiny flowers. Individual flowers lack petals and whilst the male flowers may attract insects with pollen, female flowers have neither pollen nor nectar to attract would-be pollinators and therefore trees are wind pollinated.

Trees bear heavy crops in alternate years, with little or no crop produced in the ‘off’ years due to the inflorescence primordia being aborted during heavy crops. As such, global production fluctuates from year to year but is forecast to be just short of 700,000 tonnes for the 2019/20 crop. Almost half of the produce will come from the United States and close to a quarter from Iran.

Further reading

Ferguson, L and Haviland D 2016. Pistachio production manual. University of California Agriculture and Natural Resources.

Zohary D et al. 2013. Domestication of plants in the Old World. Oxford University Press, pp. 151-152.

Louisa Hall