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Evolution and phylogenetic significance

By definition, berries have a fleshy, indehiscent pericarp, as opposed to a dry, dehiscent pericarp. Fossils show that early flowering plants had dry fruits; fleshy fruits, such as berries or drupes, appeared only towards the end of the Cretaceous Period or the beginning of the Paleogene Period, about 66 million years ago. The increasing importance of seed dispersal by fruit-eating vertebrates, both mammals and birds, may have driven the evolution of fleshy fruits. Alternatively, the causal direction may be the other way round. Large fleshy fruits are associated with moist habitats with closed tree canopies, where wind dispersal of dry fruits is less effective. Such habitats were increasingly common in the Paleogene and the associated change in fruit type may have led to the evolution of fruit eating in mammals and birds.

Fruit type has been considered to be a useful character in classification and in understanding the phylogeny of plants. The evolution of fruits with a berry-like pericarp has been studied in a wide range of flowering plant families. Repeated transitions between fleshy and dry pericarps have been demonstrated regularly. One well-studied family is the Solanaceae, because of the commercial importance of fruit such as tomatoes, bell peppers, and eggplants or aubergines. Capsules, which are dry dehiscent fruits, appear to be the original form of the fruit in the earliest diverging members of the family. Berries have then evolved at least three times: in Cestrum, Duboisia, and in the subfamily Solanoideae. Detailed anatomical and developmental studies have shown that the berries of Cestrum and those of the Solanoideae are significantly different; for example, expansion of the fruit during development involves cell divisions in the mesocarp in Solanoideae berries, but not in Cestrum berries.

When fruits described as berries were studied in the family Melastomaceae, they were found to be highly variable in structure, some being soft with an endocarp that soon broke down, others having a hard, persistent endocarp, even woody in some species. Fruits classified as berries are thus not necessarily homologous, with the fleshy part being derived from different parts of the ovary, and with other structural and developmental differences. The presence or absence of berries is not a reliable guide to phylogeny. Indeed, fruit type in general has proved to be an unreliable guide to flowering plant relationships.