What exactly makes a fruit a fruit? The rule of thumb has traditionally been if an item of produce has seeds, it's a fruit. If it's seedless, it's generally perceived as a vegetable. Plant scientists, known as botanists, define fruit as the portion of a flowering plant that develops from the ovary. That's where the plant protects and regulates dispersal of the seeds. There are many, many subcategories of fruits; depending on which parts of the flower or ovary have skin and seeds, fruits could be citrus, pepos, caryopsis, pomes, drupes, or something else. So far, so good, right? Well, you may be surprised to find out what actually falls into these categories.

A berry is a simple fruit that stems from only one flower with one ovary and lots of seeds. That's it. That means that tomatoes, pomegranates, eggplant, kiwis, and yes, even bananas, count as berries. You might not even realize that bananas have seeds — check out the little brown spots at the very center of the fruit. Those are seeds!

Berries have two subcategories: citrus and pepos. Citrus fruits are berries with a tough, oily outer layer. The endocarp, or innermost layer that surrounds the seed of the fruit, consists of succulent hairs that contain the "juice" of citrus fruit. That's right: Oranges, tangerines, lemons, and limes are all berries.

Pepos are the other type of berry, and they have a hard, rind-like outer layer around a fleshy middle layer. The most common examples of this are watermelons and cantaloupes. Surprise!

These dry, simple fruits come from a single carpel, the female reproductive organ of a flower, and don't open at maturity. This is the umbrella term for most grains: wheat, rice, corn, and barley, for instance. Yep, grains are fruits too.

Drupes tend to be a very fleshy fruit with a soft or leathery outer layer. They evolved as a way to improve the plant's numbers: Putting a big seed inside a layer of deliciousness is a great way to get animals to eat your fruit and spread your seed. Drupes include stone fruits like peaches, mangos, cherries, apricots, and even almonds and walnuts.

Most fruits that have a hard inner core count as pomes. Think apples and pears. The edible part of the fruit, including the skin, is made from enlarged floral tissue — look at the bottom of the fruit, and you can actually see a shriveled bit of flower there.

Strawberries and raspberries aren't really berries all. True berries have to be a simple fruit that stems from only one flower with one ovary and lots of seeds. Strawberries and raspberries come from a single flower with multiple ovaries, making them an aggregate fruit. Aggregate fruits form when many ovaries within the same flower form into one fruit.

If according to botanists, fruits are seed-bearing and must develop from an ovary of a flowering plant, then what is a vegetable exactly? A vegetable is classified as the other parts of the plant: the roots, leaves, and stem. By that definition, that would make things like beets, potatoes, and turnips vegetables, since they're roots, along with spinach, kale, and lettuce, since they're leaves. That would also include produce like celery and broccoli, which come from the stems of the plant.

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Want to learn about all of the different kinds of fruits and veggies out there? Check out Deborah Madison's "Illustrated Encylopedia of Fruits, Vegetables, and Herbs: History, Botany, Cuisine." We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.