Endocarp

Endocarp is the innermost part of the pericarp, the wall of a developing fruit. It lies inside the exocarp (outer skin) and the mesocarp (fleshy middle layer) and, in many fruits, surrounds the seed after fertilization. The endocarp's tissues can be hard and protective or thin and inconspicuous, depending on the species.

In stone fruits (drupes) such as peaches, plums, and cherries, the endocarp becomes a sclerenchymatous, hard stone that encloses the seed. In these fruits the woody endocarp contributes to seed protection and to the fruit's dispersal by the mechanical barrier of the stone. In other fruits, notably the coconut, the endocarp forms a hard inner shell around the seed. By contrast, many fruits have a thin or membranous endocarp that does not become a distinct hard layer.

In citrus fruits, the endocarp is the inner boundary of the pericarp and forms the walls of the juice-containing locules; it is typically not a prominent stone.

Thus, the endocarp is a variable tissue whose primary role is seed protection, with its specific form ranging from a rigid stone to a delicate lining, depending on evolutionary adaptations. The term is used mainly in fruit anatomy and plant taxonomy to distinguish the inner pericarp tissue from the outer exocarp and the middle mesocarp.