Botanists classify fruits based on the development of the flower’s ovary wall, known as the pericarp. This classification system organizes fruits into distinct groups. A drupe represents a specific botanical classification, defining a fruit that develops from a single flower with one ovary. This type of fruit is characterized by having a single seed encased within a hard, protective shell, which is why drupes are often colloquially referred to as “stone fruits.”
The Defining Structure of a Drupe
The fundamental characteristic of a drupe lies in the division of its pericarp, or fruit wall, into three distinct layers: the exocarp, the mesocarp, and the endocarp. The outermost layer is the exocarp, which is the thin skin or peel of the fruit, such as the fuzzy exterior of a peach or the smooth skin of a cherry.
Moving inward, the mesocarp is the middle layer and is typically the part consumed, often being thick, fleshy, and juicy in many common drupes. This layer provides the bulk of the fruit’s volume and flavor, containing the sugars and water that make the fruit attractive to seed-dispersing animals. The nature of the mesocarp can vary significantly, however, which leads to different categories of drupes, as seen in the fibrous husk of a coconut.
The endocarp is the innermost layer and is the defining feature of a true drupe because it is hard, stony, and lignified. This hardened layer forms the “pit” or “stone” that encases the seed, providing a robust layer of protection. The lignified endocarp ensures the seed survives the digestive tracts of animals or harsh environmental conditions until it is ready to germinate.
Identifying Common Drupe Fruits
Drupes can be broadly categorized based on the texture and composition of their mesocarp layer. The most familiar category is the fleshy drupe, which includes fruits like peaches, plums, apricots, cherries, and olives. In these examples, the mesocarp is succulent and thick, forming the majority of the edible portion surrounding the hard pit. Dates and mangoes also fall into this group, sharing the characteristic of a soft, fleshy middle layer and a single, large internal stone.
A second distinct category is the fibrous drupe, with the coconut being the most prominent example. While the coconut possesses a thin exocarp and a hard endocarp, its mesocarp is composed of thick, tough fibers, often called the husk. The part we typically consume from a coconut, the white meat and water, is actually the seed’s endosperm, which is protected by the inner, woody endocarp shell.
The third category includes dry drupes, like almonds and walnuts, where the mesocarp is thin and dries out as the fruit matures. In these cases, the outer husk splits open. What is commonly called the “nut” is either the hard endocarp (the shell of the walnut) or the seed itself (the edible part of the almond). Pistachios are also classified as drupes; the edible portion is the seed, protected by the hardened endocarp shell.
How Drupes Differ from Other Fruit Types
Distinguishing drupes from other fruit types clarifies botanical classification. Drupes are often confused with berries, but a berry is a simple fleshy fruit that develops from a single ovary and typically contains multiple seeds embedded directly within the fleshy pulp. Unlike a drupe, a true berry, such as a grape or tomato, lacks a lignified, stony endocarp surrounding its seeds.
Another category is the pome, which includes apples and pears. Pomes are accessory fruits, meaning the edible, fleshy part is not primarily derived from the ovary wall but from the enlarged receptacle of the flower. Pomes also house their seeds within a cartilaginous or papery core, which is the true pericarp, rather than a hard, stony pit.
Furthermore, many common “nuts” are actually the seeds of drupes. A true botanical nut is a dry, indehiscent fruit that does not split open at maturity, and its entire shell is the pericarp. Fruits like almonds and walnuts are botanically drupes because they develop with the characteristic three-layered pericarp.