How does an apple form as an accessory fruit?

An apple is classified as an accessory fruit because its structure involves more than just the ripened ovary. While most fruits develop solely from the ovary, an accessory fruit forms when additional floral parts—such as the stem axis or the floral tube—are retained and participate in the fruit's development.12

Specifically, the apple is categorized as a pome, which develops from a compound inferior ovary. In this process, the central part of the fruit represents the true pericarp (the ripened ovary wall), while the fleshy, edible portion is derived from the floral tube or stem axis. Consequently, the "core" of the apple contains the cartilaginous or stony endocarp, while the surrounding succulent tissue is composed of non-ovarian floral structures.2