An aggregate fruit or etaerio (/ɛˈtɪərioʊ/) is a fruit that develops from the merger of several ovaries that were separated in a single flower. In contrast, a simple fruit develops from one ovary, and a multiple fruit develops from multiple flowers. In languages other than English, the meanings of "aggregate" and "multiple" fruit are reversed, so that "aggregate" fruits merge several flowers. The differences in meaning are due to a reversal in the terminology by John Lindley, which has been followed by most English-language authors.
Not all flowers with multiple ovaries form aggregate fruit; the ovaries of some flowers do not become tightly joined to make a larger fruit. As a result, many fruits form which are commonly mistaken to be of the aggregate variety. Aggregate fruits may also be accessory fruits, in which parts of the flower other than the ovary become fleshy and form part of the fruit.
The individual parts of an aggregate fruit come in many forms. Common examples are:
The components of other aggregate fruit are more difficult to define. For example, sugar apple (Annona spp.) fruit are made up of individual berry-like pistils fused with the receptacle.