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The Abstract

Why Do Strawberries Have Their Seeds on the Outside?

Photo credit: David Lenker. Image shared under a Creative Commons license. Click for more information.

“Why do strawberries have their seeds on the outside, instead of on the inside?” That was the question one of my daughters asked recently. I had no idea, so I reached out to Chris Gunter, an associate professor of horticultural science at NC State. And the answer surprised me.

First off, strawberries don’t keep their seeds outside their fruit. Those things we think of as strawberry seeds aren’t seeds – and the big, red strawberry “fruit” isn’t technically a fruit.

In “true” fruits, like peaches*, a flower is pollinated and then the flower’s ovary swells and becomes the fruit, with the seed or seeds in the middle.

Not so with strawberries.

When a strawberry flower is pollinated, the fruit doesn’t swell. The fertilized ovaries in the flower form separate, small, dry fruits. Those “seeds” on the outside of a strawberry are actually the fruits, each of which contains a single seed.

The ripe, red, fleshy part that we think of as the strawberry “fruit” is actually swollen receptacle tissue – the part of the plant that connected the flower to the stem. When a strawberry flower is pollinated, it triggers the receptacle tissue to grow and change.

But that still doesn’t answer the question, it just changes it a little. Why are the small, dry fruits located on the outside of the red, sweet thing that we all like to eat?

The short answer is that we don’t really know which evolutionary forces caused the strawberry to develop the way that it did.

However, Gunter notes, “there are a few fundamental reasons why plants have evolved different kinds of fruits. One reason is to attract something that spreads seeds.”

A good example is the avocado. Scientists believe the avocado, with its enormous wood-like seed, evolved to be eaten by enormous animals that lived thousands of years ago. One of these animals would chow down on some avocados and either leave partially-eaten fruit (and its seed) nearby, or the seed would pass all the way through the animal and be left behind in its waste.  Since those giant beasts are no longer with us, avocados are now dependent on human intervention to spread their seeds.

“A second evolutionary approach is for plants to find ways for their fruit to disperse on their own,” Gunter says. “For example, they may fly in the wind, like a dandelion, or be moved by the water, like a coconut.”

The third option is for a plant to find ways for a fruit to deter animals from eating it. “For example, the gingko fruit smells putrid,” Gunter says. “The goal there is for the fruit to not get eaten, so that the seed can rely on the fruit’s nutrients to support its growth.”

Presumably, the strawberry went for evolutionary option number one – attract something to spread the seeds. But we don’t know the specifics.

*Note: The example for a true fruit was originally an apple. And then someone told me that apples are not true fruits either. In fact, they belong to a group called pseudo-carps, or false fruits. That’s because the part we think of as the fruit is made from plant parts other than the ovary. And – surprise – the fleshy part of an apple is also made of the receptacle tissue. In other words, it was just about the worst example I could have thought of to hold up as the alternative to a strawberry. But now I know that – and so do you!

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  1. So, you’re saying the plant has thoughts about how it should spread it’s seed? It developed itself to be eaten by huge creatures??? That’s amazing!!!

  2. Nearly all of the edible portions of an apple is hypanthium although a small portion may be from the receptacle and ovary. The hypanthium is an area of fused sepals, petals and stamen; the receptacle would be where they all attach at the pedicel. Fruits are nearly impossible to figure out without looking at the flowers. This is true also with your strawberry example, where a swollen receptacle is the vertebrate animal attractant but without a flower to a look at, it’s not easy to see. In strawberries, the green leaf-like structures are sepals, and between them and the receptacle are the persistent stamens. Lastly, in strawberry, the achenes (incorrectly called seeds) have a style and stigma still attached. The little “hairs” at the bottom of the blender are those.

    Wayne Armstrong at Palomar College has an excellent site with a few pages of this sort of information on it.

  3. Thanks! I didn’t know I have been eating the “womb” of the tree, and not the “baby” of the tree…. I guess if a mammal would create a nutrient rich environment for the fertilized egg to be enrich during gestation … In similar fashion, the seeds sits on a nutrient rich enviro, and the alternate purpose is to nourish the animal that eats it, in exchange to be turn up in the Poop that nourish it.

  4. My hypothesis: the strawberry was consumed from within during its evolution (nice, fat, tasty fruit) by some type of worm that, in affect, scattered the fruit (seeds) attached on the outside. OK, that’s the basis, I will need a grant to prove / disprove its validity. Any takers?

  5. Why is there rancor over God vs. evolution?
    The truth is that the answer is BOTH as God and evolution are not in opposition to each other nor are they mutually exclusive. There is a creator and his amazing creation, which includes our earth, has evolved and continues to do so. Darwin’s theory is flawed but that does not negate the reality of evolution in our world and evolution’s existence does not prove there is no God.

  6. Jeff, first, God is evolution. And second, strawberries weren’t originally designed to provide us with something delicious and nutritious to enjoy. Strawberries were originally, in their wild state, much smaller than the ones we cultivate today, barely bigger than peas. They were designed to be eaten by birds, who then carried their seeds hither and yon. Large strawberries were created through selective breeding by humans.

    1. Very interesting Erik! Do you know when humans started the breeding of strawberries? Was it thousands to millions of years ago or more recently? Like in the past 300 years? Very curious after reading your article.

      I do see that strawberrie could be much smaller. We planted some in our landscaping a few years ago and they have dominated the area. The strawberries are much smaller than what we buy in the stores. My grandchildren and the birds love eating them.

      1. Erik,
        You can try to leave God out of creation, but some of us believe/know otherwise.
        Don’t unload your Darwin religion on us.

        Jesus is Lord and Creator, and one day all will know and confess.

        1. Well Jesse, I think the operative word should be “believe” otherwise. Which, of course, is totally your prerogative. It is interesting how intolerant religion can be at times when those that have no ill-will towards you and your beliefs are slammed for their own… Hopefully someday those that live on this planet will learn to practice some mutual respect and tolerance.

          Thanks Matt Shipman for the light and educational article – learning new things every day!

          1. OMG I was thinking the EXACT thing after I read the comment by Jesse. Wow! It’s kind of like “can’t we all just get along”??? Thank you Erik for ASKING Jesse to consider that people can get along without necessarily AGREEING…point well put.

      2. If I plant those tiny seeds will a plant come up that will produce edible strawberries? Thank you all.

    2. I agree with you…. forget the Fairy Tales…get real! Even as a lay person I knew that…what do they learn in school here? In Europe, the first thing you learn is all about the local fruits, trees, veggies, mushrooms etc… most important to know what and what not you can eat in the wild, and the wild, original strawberries still grow in European forests. They are tiny and very sweet…much better flavor than any man made ones… we picked them as kids!

  7. You can have your evolutionary theories, but my short answer is that God designed and created the strawberry to give us something delicious and nutritious to enjoy.

    1. People read the comments, and do you want them to wonder if NC State news readers are uneducated? Please don’t trivialize the research done by students and professors here and in the rest of the world by such comments.

      1. As a former NCSU graduate, and insatiably curious about both science and religion, your response could appear equally uneducated and trivial. Did you make any attempt to understand his point of view, or is a religious response always assumed to be uneducated? Einstein once said “The more I study science, the more I believe in God.”

        1. Yes, his response was uneducated because it ended the search for truth with the common cheap excuse of ‘God did it that’s all I or anyone else ever needs to know.’

          I’m a Christian and a scientist and that excuse has plagued mankind for years limiting our understanding of the universe and revelling in its own ignorance and is simply unacceptable in an enlightened age.

          Had Copernicus accepted such short sighted thinking Einstein would have never been able to make the quote you mentioned because we’d all still believe the universe rotated the Earth. We’d still think rivers were formed from the tears of Osiris and Thunder was Thor showing his displeasure. Without people like me Christianity itself may have never been born as all the other mythologies answered the mysteries of our universe with the same, creative but lazy excuse of “God did it, that’s all you need to know”

          Simply put, religion is great and trying to live up to Jesus example is a lofty goal indeed but this is an article about science and unraveling the mysteries of the universe and so entering a conversation about biology and trying to end it with a blunt and ignorant, ‘god did it and that’s all that matters.’ Is simply rude and has no place here and I would say the same thing if we were on a religious website and same jrrk came along groaning, ‘bah god isn’t real, science is the only true answer!’

          It’s simply rude and a provocative attack that shouldn’t happen. Frankly I’d like to add that if a website theorising why a strawberries ‘seeds’ are on the outside is enough to threaten your religious beliefs to the point you have to lash out and proclaim ‘nuh uh! God did it’ Your religious beliefs don’t really have much of a leg to stand on if they are so easily threatened now do they?

          This just proves that insecure theists who worship ignorance are as annoying and shortsighted as any militant atheist on the internet.

          Take care, but seriously folks pick more worthy battles with better hills to die on than a board explaining strawberries. If your answer to everything is ‘God did it.’ Than why are you even here if not to pick a fight? Sheesh, expand your horizons a bit and open your minds.

          1. The universe indeed rotates around the still earth. Check the documentary film “The Principle” and argue with Max Tegmark, the Swedish-American cosmologist and professor at MIT and the scientific director of the Foundational Questions Institute if you disagree.

    2. I agree. Why do scientists believe that evolution is so “clever”, but not believe in an intelligent Creator? Look at the bumblebee – it’s the only creature with such a body weight–wing span ratio that can fly, but this is okay with evolutionists. Their unbelief blinds them.