In the plant reproductive process, seeds form inside the ovary and, after pollination, this becomes the fruit we are familiar with. In contrast, some plants appear to carry their seeds on the outside of the fruit, however, this simply isn't true.
Generally, people accept 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 little biology lesson will have you rethinking everything you thought you knew about the strawberry.
The 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.
Aggregate fruits form from a single flower. The strawberry itself is actually the plant's flower and that desirable sweet red flesh is called the receptacle, which is located below the ovary. The receptacle swells in size to attract animals who will eat them and scatter the "true fruit."
The "true fruits" of the strawberry are actually what we think of as the seeds. Technically, those small, yellow seed-like pieces are called achene and each is a fruit. Inside each achene is the actual strawberry seed.
If the seeds are that 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 they 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 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.
What About Cashews?
While most of the talk about fruits with visible seeds centers on the strawberry, we cannot forget the equally deceptive cashew. On the tree, it appears that the cashew grows on the outside of a fruit which looks much like an apple. However, this is another case of the receptacle swelling to promote the true fruit, which is called drupes.
The cashew we eat is actually the pit inside a shell. It is rather similar to stone fruits like nectarines and cherries, except the pit is the desired food source. It's also interesting to note that the cashew shell has a toxicity similar to poison ivy, which is why they're always sold shelled.