The pistachio tree (Pistacia vera) is a small, long-lived, deciduous tree highly adapted to arid and semi-arid regions, with a native range spanning from Central Asia to the Middle East. This resilient plant is cultivated primarily for its edible seed, which is borne on trees that can maintain productivity for centuries. Understanding the visual characteristics of the pistachio tree provides a clear picture of this unique species.
Overall Physical Characteristics
The pistachio tree is typically a small to medium-sized tree, often reaching a height of about 20 to 30 feet (6 to 10 meters). It is characterized by an open, spreading, and rounded canopy that provides a sturdy silhouette. Cultivated trees are often pruned to maintain a manageable size, but they naturally possess a somewhat bushy habit, especially when young.
The trunk of the mature tree is relatively short and thick, supporting the wide, outward-growing branches. The bark is rough and gray-brown, often developing a deeply furrowed or shaggy texture as the tree ages. The tree’s deep, extensive root system, classified as a phreatophyte, allows it to thrive in dry conditions and withstand long periods of drought.
Foliage and Branch Structure
Pistachio trees are deciduous, meaning they shed all their leaves in the autumn and remain bare through the winter months. The leaves are compound, typically growing to about 4 to 8 inches in length, and are made up of thick, leathery, dark green leaflets.
The pinnately compound structure usually consists of three to five leaflets. Before dropping, the foliage provides a visual display, turning into distinctive shades of yellowish-red and orange-red in the fall. The branches themselves can appear somewhat twisted, contributing to the tree’s rugged, desert-adapted look.
Sexual Dimorphism
Pistachio trees are dioecious, indicating that individual trees are distinctly male or female, and they bear only one type of flower. Both male and female flowers are small, lack colorful petals, and are generally inconspicuous, appearing in clusters called panicles or racemes in the spring. Since the tree relies on wind for pollination, the flowers do not need to attract insects.
The most visible difference between the sexes appears during the flowering period. Male trees produce pollen-bearing flowers in tight, clustered inflorescences, designed to release large amounts of pollen into the wind. Female trees bear flowers that develop into fruit, and their inflorescences are typically more loose and open to easily capture the airborne pollen. Only the female trees will produce the commercial nut, requiring the presence of a male tree nearby for fruit set.
The Appearance of the Developing Nut
The fruit of the female pistachio tree is botanically classified as a drupe, not a true nut, similar to a peach or cherry, though the edible part is the seed inside. These drupes grow in dense, heavy clusters that visually resemble bunches of grapes hanging from the branches. Each developing fruit is oblong and initially covered by a soft, thin outer hull, which is a pale greenish color.
As the fruit ripens through the summer, the outer hull undergoes a distinct color transformation, changing from green to a reddish or pinkish hue. When the seed inside is fully mature, the hard, light-colored shell (endocarp) splits open longitudinally along the suture. This natural splitting is a key indicator of ripeness and reveals the beige, bony shell that encases the edible green kernel.