Mad About Science: Watermelons

By Brenden Bobby
Reader Columnist

As you’re reading this, I’m currently living my best life as an international jet setter.

By that, I mean I’m in Vancouver, B.C., checking out the library and Science World.

Before I left, I made sure to inundate the Reader staff with plenty of articles to stuff the pages while I’m gone. Today, we’re going to take a look at my favorite summertime treat.

Watermelon, Citrullus lanatus, is a flowering plant that produces large, weighty berries that are very sweet with a thick protective rind. You read that right: The fruit of a watermelon is a berry, at least according to botanists.

In botany, a berry is defined as a fleshy fruit without a pit or stone that is produced from one flower that contains one ovary. By this same definition, raspberries and strawberries are not berries at all.

A Giovanni Stanchi painting from the 17th century showing how breeding has changed the look of a watermelon in modern times. Courtesy image.

Try telling all of that to chef Christina Tosi while making a watermelon and strawberry soufflé, and it will become immediately apparent that botanical definitions and culinary definitions are two markedly different things.

Another quirk of botany is referring to the plant by the name of the fruit. A bush that grows blueberries is a blueberry, even if you may hear it referred to as a “blueberry bush” or “blueberry plant.” The same is true of the watermelon.

The watermelon is a vining plant that loves to sprawl out and take over a wide space. There’s a reason that watermelons have adapted to do this. Vining plants are brilliant natural adaptations that have traded stability for maximized growth. Things like grapes, squash and melons use vines, which are just the plant’s stem, to reach outward and use other plants as their support. This means the plant can devote less energy to creating a structure to bear fruit, and more energy to creating the fruit and maximizing its chances of survival and reproduction.

Let’s look at an example of how this works by comparing an apple to a watermelon. An apple’s fruit has a very thin rind, so it needs to be high off the ground while it’s developing, or it’s likely to be eaten. 

To accomplish this, the tree devotes a tremendous amount of energy and resources from sunlight, water and the soil to build a thick and powerful trunk and branches to grow apples up in the air and away from crawling pests. Because of the energy being devoted to growing the tree, and since the apple is now suspended in the air and subject to gravity, the apples need to be smaller and lightweight.

A watermelon doesn’t have a thick and powerful trunk. Instead, it will vine outwards to anchor itself to other plants. The fruit has a thick rind to protect the seeds from hungry fauna, and the plant doesn’t have to worry about fighting gravity to support the fruit. This creates the perfect conditions to create massive berries that are loaded with seeds, giving the plant a great chance at making more plants in the spring. This is true of squash as well, and is among the reasons we see massive pumpkins and zucchini in the fall.

These plants are an ancient cultivar that have vined their way across much of the Eastern Hemisphere during antiquity. We’ve traced the plant’s genes to an ancestor in southern Africa that was specially adapted to hoard water in a dry climate. There are historical records of the Indigenous people of this area roasting the seeds from this plant, similar to pumpkin seeds and sunflower seeds today. 

The flesh of this ancestor plant was believed to be very tough and bitter, a far cry from the watermelon we know now. Around 4,000 years ago, this plant traveled north into Egypt, where it was selectively bred to more closely resemble the delicious sugary watermelon we’re familiar with. It wouldn’t take long for the plant to make its way into Europe, where a wetter climate helped it balloon into becoming a red and green giant.

We can take a rare glimpse into the watermelon’s ancestral history, thanks to Renaissance paintings. One in particular shows a curious example of a watermelon that seems to have pockets of red flesh suspended between ridges of white rind. 

Italian artist Giovanni Stanchi created a still-life painting during the 17th century that depicts a carved watermelon. Curiously, this melon seems to have funky red spirals and familiar black seeds scattered throughout. The spiraling flesh looks like a symptom of hollow heart, an affliction that affects watermelons that were not properly pollinated, but the presence of developed seeds dispels this theory. This leads us to believe that either an unusual breed of watermelon existed in Italy during the 1600s, or the painter took a few creative liberties for the sake of representing an identifiable fruit.

Another brain-boggling tidbit of information that may change your view of watermelons forever is this: the juicy red flesh that we love so much is actually the placenta. This sugary red tissue is designed to help support the seeds and offer them a jumpstart when the body of the melon begins to decompose. As gross as that sounds, consuming plant tissue is a completely different organic process than consuming animal tissue, and something we should all do regularly.

A final factoid for your barbecue is the most important answer of all: why watermelons are red. Red is a somewhat uncommon color in the plant world, as plants often prefer green chlorophylls to help with photosynthesis. The red of a watermelon’s flesh comes from something called lycopene, which is a carotenoid, or a red pigment that’s found in other plants like tomatoes and carrots.

Luckily for us, watermelons taste nothing like either of those, as most of the taste involved comes from the sugars of the giant berry.

Stay curious, 7B.