A plum is not a berry, though the confusion is understandable because botanical classification often contradicts common language. While the culinary term “berry” is loosely applied to small, fleshy, sweet fruits, science uses strict criteria based on structural development. Botanically, a plum is classified as a drupe, which is structurally distinct from a true berry.
Defining the True Berry
A true berry develops from a single flower containing one ovary, where the entire ovary wall matures into a fleshy fruit called the pericarp. The pericarp is composed of three layers: the outer skin (exocarp), the middle fleshy part (mesocarp), and the innermost layer (endocarp). In a true berry, all three layers remain fleshy when ripe, resulting in uniform softness. True berries contain multiple seeds embedded directly within the soft pulp, lacking any hardened internal structure. Examples of fruits that fit this botanical definition include grapes, tomatoes, and bananas.
The Defining Characteristics of a Drupe
Plums are classified as drupes, a type of simple fleshy fruit distinguished by its unique internal structure. Like a berry, a drupe develops from a single flower ovary, and the outer layers of the pericarp (exocarp and mesocarp) become soft and fleshy. The major difference lies in the endocarp, the innermost layer of the fruit wall. In a drupe, the endocarp hardens into a protective, stony shell, commonly known as the “pit” or “stone.” This hard layer completely encloses the single seed inside, which is why drupes are often called “stone fruits.” Other common examples include peaches, cherries, olives, and almonds.
Common Misclassifications in Fruit Terminology
The divergence between scientific classification and everyday language is the main source of confusion. Many fruits commonly called berries do not meet the botanical criteria, while many unexpected fruits actually do. For instance, strawberries, raspberries, and blackberries are not true berries; they are classified as aggregate or accessory fruits. A strawberry is an accessory fruit because its fleshy, edible part develops from the swollen receptacle of the flower, not the ovary. Conversely, fruits like watermelons, cucumbers, and bell peppers are all botanically considered berries because their entire ovary wall ripens into a fleshy pericarp with multiple seeds embedded in the flesh.