In the plant reproductive process, seeds form inside the ovary, where they are pollinated and grow into the fruit we are familiar with. While some plants appear to carry their seeds on the outside of the fruit, this simply isn't the case. It is commonly believed that the strawberry is the only fruit that wears its seeds on the outside. The strawberry is deceptive, though. Those tiny yellow specks are not really the seeds, and that sweet flesh we love is not the actual fruit. A brief biology lesson will help you rethink everything you thought you knew about the strawberry (and some other familiar fruits).
Anatomy of the Strawberry
The strawberry is a fruit, but it's not classified in a way you might expect. Despite its name, the strawberry is not a "true berry" because it lacks the thin skin and pericarp (three layers formed from the wall of an ovary) that botanically define a berry. True berries include grapes, cranberries, and even tomatoes and eggplant.
Instead, strawberries are what is known as an aggregate fruit. Raspberries and blackberries fall into this category as well, and all of these fruits are in the same family as the rose, called Rosaceae.
Aggregate fruits form through the merging of multiple ovaries within a single flower. The strawberry grows from the plant's flower, and that sweet red flesh growing below the hull (or calyx) is called the receptacle. The flower’s white petals reflect ultraviolet light to attract bees, who will pollinate the fruit. The receptacle swells in size to attract animals who will eat them and scatter the "true fruit."
Fruit, Not Seeds
The "true fruits" of the strawberry are actually what we think of as the seeds. Technically, those small, yellow seed-like bits are called achenes, and each is a fruit. Inside each achene is the actual strawberry seed. An average-sized strawberry holds about 200 achenes.
How Strawberries Grow
Given that the seeds inside the achenes must be tiny, you might wonder how strawberry plants grow so well. The catch here is that the strawberry plant doesn't necessarily rely on seeds, though the seeds can produce a new plant.
Instead, the majority of strawberries are propagated from the runners or clones. Runners grow and stretch out of the main plant until they find new ground where they can root themselves. Each mother plant can send out multiple runners, and each runner can have multiple new strawberry plants. This aggressive behavior makes up for the diminutive size of the plant's difficult-to-grow seeds.
At maturity, these popular berries (or, rather, popular aggregate fruits) pack a nutritional punch and are among the most healthful foods out there. A cup of strawberries provides more than the average adult’s daily allowance of vitamin C as well as valuable antioxidants.
What About Cashews?
While most of the talk about fruits with visible seeds centers on the strawberry, we cannot forget the equally deceptive cashew. The cashew tree can grow to over 40 feet and has large, bright green leaves and bright pink flowers. And although it appears that the cashew nut grows from fruit that looks like an apple or a bell pepper, this is another case of the receptacle swelling to promote the true fruit—called a drupe.
A drupe is a type of stone fruit that includes peaches, cherries, nectarines, and plums. The drupe of a cashew tree is kidney-shaped and grows along with a larger form called a cashew apple. Inside the drupe is its tasty seed, the thing we call the cashew “nut.” In contrast to other drupes, like peaches, the seed of a cashew drupe is the desired food source, rather than the "pit."
It's also interesting to note that the cashew shell has a toxicity similar to poison ivy, which is why cashews are always sold shelled. And while you can buy a bag of “raw” cashews, they aren’t really raw—they’ve been roasted in their shells and then steamed to make them safe to eat.
One more bit of cashew trivia: The kidney-shaped drupe forms first, followed by the developing pedicel that becomes the cashew apple. Cashew apples are eaten fresh and are used to make jams and juices. They are also pressed for their juice, which is distilled to make alcohol. The cashew apple is fragile and is rarely exported in its natural form, but it’s actually the favored part of the cashew tree in many areas of the world.