Despite its name, the strawberry isn't a true berry. Neither is the raspberry or the blackberry. But the banana is a berry, scientifically speaking, as are eggplants, grapes and oranges.

So what's the deal? Why are berries so very hard to define?

The discrepancy in berry nomenclature arose because people called certain fruits "berries" thousands of years before scientists came up with a precise definition for the word, said Judy Jernstedt, a professor of plant sciences at the University of California, Davis. Usually, people think of berries as small, squishy fruit that can be picked off plants, but the scientific classification is far more complex, Jernstedt said.

Related: What's the difference between a fruit and a vegetable?

Judy Jernstedt

Professor of plant sciences at the University of California, Davis.

Judy Jernstedt is a professor of plant sciences at the University of California, Davis. Jernstedt specializes in the structure and development of crop plants, plant anatomy and evolutionary morphology, among others. Jernstedt received a doctorate in Botany from the University of California, Davis in 1979, and a master's in Plant Physiology from the same university in 1974.

What is a berry?

In order to be considered a berry, a fruit must develop from a flower that has one ovary. (Image credit: udaix/Shutterstock.com)The same layered structure appears in other berries, including the banana and watermelon, although their exocarps are a bit tougher, taking the form of a peel and a rind, respectively. (The suffix "carp" comes from the word "carpel," which refers to the pistil, the female organ of the flower, Jernstedt said.)

In addition, to be a berry, a fruit must have two or more seeds. Thus, a cherry, which has just one seed, doesn't make the berry cut, Jernstedt said. Rather, cherries, like other fleshy fruit with thin skin and a central stone that contains a seed, are called drupes, she said.

Moreover, to be a berry, fruits must develop from one flower that has one ovary, Jernstedt said. Some plants, such as the blueberry, have flowers with just one ovary. Hence, the blueberry is a true berry, she said. Tomatoes, peppers, cranberries, eggplants and kiwis come from a flower with one ovary, and so are also berries, she said.

Other plants, such as the strawberry and the raspberry, have flowers with more than one ovary.

"Raspberries have those little subunits," Jernstedt said. "Each one of those little subunits comes from an individual ovary. And those subunits are actually [called] drupes."

Each drupe contains a seed; that's why wild raspberries and blackberries are so crunchy, according to Jernstedt. Because these types of fruit consist of so many drupes, they're called aggregate fruit, Jernstedt said. A strawberry is also an aggregate fruit, but instead of having multiple drupes, it has multiple achenes, the little yellow ovals on the fruit's surface, which each contain a seed.

Like other berries, bananas are composed of three fleshy layers: the outer skin, the mushy middle and the innermost part with the seeds. (Image credit: Shutterstock.com)Oranges are a subtype of berry called hesperidium, said Courtney Weber, a berry breeder at Cornell University in New York. Like other berries, oranges have three fleshy layers, have two or more seeds, and develop from one flower with one ovary. But citrus fruits contain distinct segments, a property that differentiates these fruits from other berries and gives them the subtype status, Weber said. (The number of sections is related to the number of carpels, Jernstedt said.)

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In all, berry categorization "s kind of chaotic," Jernstedt said. "And the scientists feel that way too. There are always attempts to impose some order on fruit classification. But this has been going on for a couple of centuries, so don't hold your breath that it's going to be solved soon."

In other words, it can be difficult to classify nature's many fruits, which evolve without a thought about how scientists will view them.

"Flowering plants have devised a number of ways to produce seed and to get that seed distributed," Webber told Live Science. "Having the fleshy fruit types that we eat is just nature's way of getting animals to eat this fruit and seed and distribute them."