The cashew, derived from the tropical evergreen tree Anacardium occidentale, presents a fascinating botanical puzzle. What appears to be the fruit is not a true fruit, and the part commonly called a nut is actually a seed. The plant structure is unique, with two distinct edible parts developing together: a fleshy, brightly colored structure and a hard, kidney-shaped shell attached below it. Understanding the precise botanical terms for these components settles the debate over whether the cashew is a fruit or a nut.
Defining the Cashew Apple
The bright, colorful, pear-shaped structure that develops first is known as the cashew apple. This fleshy part is classified as an accessory fruit, or pseudofruit, because it is not the true fruit of the plant. Accessory fruits develop from plant tissue other than the flower’s ovary, such as the pedicel (flower stalk) and the receptacle of the cashew flower.
This accessory fruit can ripen into a yellow or red structure that is typically 5 to 11 centimeters long. The cashew apple is notably juicy, containing a high water content, and is an excellent source of vitamin C. Despite its nutritional value, the apple is highly perishable and often possesses an astringent taste due to high tannin levels, leading to its underutilization in many regions where cashews are grown.
The True Fruit and Botanical Classification
The true fruit of the cashew tree is the hard, kidney- or boxing-glove-shaped structure that is attached to the bottom of the cashew apple. This structure is a type of simple fruit known as a drupe. A drupe is characterized by a hard inner shell, or endocarp, that surrounds a single seed. Unlike most drupes, which have a fleshy exterior, the cashew’s true fruit is dry and contains the seed we consume within its shell.
The edible portion known as the cashew “nut” is botanically the single seed contained within this drupe. The shell of this true fruit is complex, consisting of three distinct layers collectively called the pericarp. Between the hard inner endocarp and the outer exocarp lies a resinous layer called the mesocarp. This mesocarp contains Cashew Nut Shell Liquid (CNSL), a highly caustic and toxic substance composed primarily of anacardic acids. This toxic resin necessitates specialized, high-heat processing to safely remove the shell before consumption.
Why Cashews Are Called Nuts
The common use of the word “nut” to describe the edible cashew kernel is based on culinary tradition and convenience, not botanical accuracy. Botanically, a true nut is a dry, indehiscent fruit with a hard shell, such as a hazelnut or an acorn. Since the cashew is the seed of a drupe, it does not meet this strict definition.
Culinary classification often groups any large, oily kernel used in cooking into the “nut” category, regardless of its scientific origin. Cashews fit this description due to their high content of fat and protein, which provides a rich flavor and versatile texture similar to true nuts. Regulatory bodies often classify cashews as “tree nuts” for practical reasons related to nutrition and potential allergen management. While the cashew is technically a drupe seed, the common use of the term “nut” is widely accepted within the context of cooking and commerce.