Ask Dr. Universe: Fruit of vegetable? That depends on how you classify it

Dr. Universe: Why are some veggies called fruits because of their seeds? – Valerie, 10, New Mexico

Dear Valerie,

Every summer I grow peppers in my garden. I always thought they were vegetables. But you’re right that my peppers have gobs of seeds like fruits do.

To figure out what’s going on, I talked with my friend Jacob Blauer. He’s a plant scientist at Washington State University.

He told me that whether something is a vegetable or fruit depends on what part of the plant it comes from.

“Plant products that come from plant parts like roots, leaves or stems are veggies,” Blauer said. “If they come from a flower and bear seeds, they’re a fruit in botanical and scientific terms.”

Botany is the plant science that looks at the structures that make up a plant’s body. Like its roots, leaves and stems.

When you chow down on a carrot, you’re eating the carrot plant’s root. When you eat lettuce, you’re eating the lettuce plant’s leaves. When you chomp on some celery, you’re eating the celery plant’s stem. These are all vegetables.

But my peppers don’t come from the pepper plant’s roots, leaves or stem. A pepper forms when my pepper plant reproduces through a flower. That’s how it makes seeds that will become baby plants.

After a flower forms, pollinators like the wind or insects come along. They move pollen from one part of the flower to another part of the flower. Or between flowers. Soon, a teeny, tiny pepper full of seeds begins to grow.

Pollinators move pollen from the anthers to the stigma . Sometimes that happens within the same flower. Sometimes they move pollen between different flowers.

The whole point of the pepper is to move those seeds to a new place. In the wild, birds gobble up the peppers and seeds. Then, they fly off and poop out pepper seeds somewhere else. Those pooped-out seeds can grow into new pepper plants.

Since peppers come from a flower and have seeds, botanists call them fruits. Even though they’re not sweet or tart like most fruits. There are lots of fruits like that – like tomatoes, squashes, eggplants, cucumbers and avocadoes.

As a scientist, I think it makes lots of sense to classify plant foods based on botany and plant science. But humans are complicated animals. So, nutrition experts sometimes classify a plant food based on other traits, too. Like how sweet or savory it is. Or how it’s usually cooked.

That’s why some fruits – like my peppers – wind up in the vegetable group. If that seems a little confusing, that’s because it is. It can make it challenging for scientists who work with plants that are classified in more than one way. It can also make it harder for food programs to get the most nutritious foods to people – because there are lots of opinions on how to classify plant foods.

Blauer told me that potatoes have a classification problem like my peppers do. According to science, they’re vegetables. They’re a plant part that grows underground called a tuber. That’s an underground branch that stores vitamins and complex sugars called starches.

But sometimes potatoes get kicked out of the vegetable group and called less nutritious because of those starches. That’s a shame because the humble spud is so nutrient-dense that it’s fed hungry people throughout history and helped shape the world we know today.

When it comes to nutrition, it’s a real peeler of strength.

Sincerely,

Dr. Universe

Adults can help kids submit a question at askdruniverse.wsu.edu/ask.