The common term “nut” often causes confusion because it is used to describe many different edible items that grow on trees. People frequently assume that any hard-shelled kernel is a true nut, but botany classifies these edibles differently. The distinction lies in how the fruit develops and the specific parts of the plant we consume. This article clarifies which popular tree-grown edibles are botanically true nuts and which are technically seeds.
Defining the Tree Nut: Botanical Versus Culinary Use
The culinary definition of a nut is broad, referring simply to any large, oily kernel found within a hard shell. This common usage encompasses a variety of foods, including certain seeds and legumes. This definition is based purely on the edible part’s appearance and texture, not its biological origin.
Botanically, a true nut is a specific type of dry fruit that possesses a hard, woody outer wall, known as the pericarp. This fruit is indehiscent, meaning it does not open naturally at maturity to release the single seed it contains. The entirety of the hard-shelled item is the fruit itself, with the edible kernel being the seed inside.
Most items commonly called nuts, such as almonds or pecans, are not true botanical nuts, but are instead classified as the seeds of drupes. A drupe is a type of fleshy fruit, like a peach or a cherry, that contains a hard pit or “stone” surrounding the seed. In these cases, we eat the seed found inside the pit, not the entire fruit.
Examples of True Nuts Growing on Trees
Chestnuts (Castanea) are a clear example of a true botanical nut. The fruit develops within a prickly, cup-shaped structure called a cupule or involucre, which protects two or three nuts inside. When the fruit matures, the cupule splits open, allowing the hard-shelled nuts to fall to the ground.
Hazelnuts, including filberts (Corylus), also meet the botanical criteria for a true nut. The fruit is enclosed in a husk formed from the fused bracts of the flower. The shell of the hazelnut is the hard, woody wall of the fruit, surrounding a single seed.
Acorns, the fruit of oak trees (Quercus), are another example of a true nut, although they are not widely consumed by humans. The acorn is a single-seeded, indehiscent fruit with a tough shell. It is partially enclosed by a characteristic scaly cap known as the cupule.
Common Tree Nuts That Are Botanically Seeds
Walnuts and pecans are popular commercial “nuts” that are technically the seeds of a drupe. The tree initially produces a fruit with a fleshy, green outer layer, known as the husk. This husk is the exocarp and mesocarp of the fruit.
As the fruit matures, the husk dries out and splits open, revealing the hard, wrinkled shell underneath. This hard shell is the endocarp, or the pit of the drupe. The edible kernel we consume is the seed protected inside this stony pit.
Almonds are also classified as the seed of a drupe (Prunus genus), related to peaches and cherries. The almond tree produces a fuzzy, green fruit that looks similar to a small, unripe peach. This outer layer is called the hull.
When the almond fruit ripens, the hull dries and splits open along a seam. Inside the hull is the hard pit, which is the familiar almond shell. The seed nestled inside this shell is the edible almond, meaning we eat the seed after discarding the fruit’s outer layers and pit.
Cashews present a unique case, as they are the seed of a fruit that grows outside of the main fruit body. The cashew tree produces a fleshy, pear-shaped structure known as the cashew apple, which is an accessory fruit. The actual cashew fruit is a kidney-shaped structure that hangs from the bottom of this apple.
The edible cashew kernel is the seed found inside this kidney-shaped fruit. This seed is surrounded by a shell containing caustic oils, requiring careful processing before it is sold. The cashew is botanically a seed attached to the base of the fleshy cashew apple.