Watermelons are, in the strict botanical sense, berries. More precisely, they belong to a specialized subcategory of berry called a pepo, which is defined by a fleshy interior surrounded by a tough outer rind that develops entirely from the ovary wall of a single flower. The classification sounds absurd when you picture a 10-kilogram watermelon sitting next to a blueberry, but the two share the same underlying fruit anatomy that botanists care about. How the watermelon earned this title, and why so many familiar “berries” actually are not, turns out to be a surprisingly interesting story about what words mean when scientists use them versus when the rest of us do.
What Botanists Actually Mean by “Berry”
In everyday English, a berry is a small, round, juicy fruit you can pop into your mouth. In botany, the word has a much more specific and technical meaning that has almost nothing to do with size or sweetness. A botanical berry is a fleshy fruit that develops from a single ovary of a single flower, contains seeds embedded in the flesh, and does not have a stone or pit layer surrounding those seeds. The outer skin, the fleshy middle, and the inner seed-bearing region all originate from the ovary wall, which botanists call the pericarp.
Under that definition, watermelons qualify easily. A watermelon develops from a single flower with a single ovary. Its seeds are scattered throughout the fleshy interior rather than being locked inside a hard pit. And the entire structure, from the green rind to the red flesh to the thin layer around each seed, derives from the ovary wall. The fact that the whole package weighs several kilograms instead of a few grams is irrelevant to the classification. Size never enters the botanical definition.
This is also why strawberries, raspberries, and blackberries are not true botanical berries, despite having “berry” right in their names. Strawberries are accessory fruits where the fleshy part comes from the receptacle tissue rather than the ovary. Raspberries and blackberries are aggregates of many tiny stone fruits (drupelets), each with its own hard seed coat. Meanwhile, grapes, bananas, tomatoes, and eggplants all meet the botanical berry definition perfectly. The disconnect between common usage and scientific classification is one of the most reliably surprising facts in plant biology.
The Pepo, a Berry in Armor
Watermelons are not just generic berries. They belong to a subtype called a pepo, which is essentially a berry that has developed a hardened outer rind. The term comes from the Greek word for a type of melon, and it describes a modified berry with a tough exterior and a soft, fleshy interior, a structure formally described as a hard rind enclosing a soft fleshy mesocarp.1Journal of Experimental Botany. The genetic basis of fruit morphology in horticultural crops: lessons from tomato and melon The rind is not a shell or a husk added on from the outside. It develops from the same ovary tissue as the flesh, just with cells that become thicker-walled and more rigid as the fruit matures.
That rind is a genuinely impressive piece of natural engineering. In one study of watermelon cultivars, the rind measured about 1.5 centimeters thick on average, and the force required to puncture it varied depending on the angle of penetration, ranging from roughly 21 to 24 newtons.2Advances in Agricultural and Food Research Journal. Physical and Mechanical Properties of Watermelon Rind That might not sound like much in engineering terms, but for a fruit sitting on the ground in a hot climate, it provides real protection against physical damage, moisture loss, and soil-dwelling organisms. The rind is what separates a pepo from a standard berry like a grape or tomato, whose skin is comparatively thin and fragile.
What makes the pepo classification interesting is that it highlights a spectrum within the berry category. At one end, you have soft-skinned berries with virtually no rind. At the other, you have pepos whose outer layers have become so tough that you need a knife to get through them. The underlying anatomy is the same. The difference is how much the outer portion of the pericarp has lignified and hardened.
Watermelon’s Botanical Relatives
All pepos belong to the Cucurbitaceae family, sometimes called the cucurbits or gourd family. This is a large and diverse plant family, and its members include many of the fruits and vegetables you already know. Cucumbers, zucchini, pumpkins, bottle gourds, bitter gourds, and various luffas all belong here, along with melons, horned cucumbers, and, of course, watermelons.3IntechOpen. Overview of Cucurbitaceae Families
Every one of those fruits is technically a pepo, which means every one of them is technically a berry. The pumpkin you carve at Halloween, the cucumber in your salad, the zucchini on the grill: all berries. This tends to be the point where people start suspecting that the botanical definition of “berry” is simply too broad to be useful in ordinary conversation, and they are not entirely wrong. But within plant science, the classification captures something real about shared developmental biology. All these fruits grow from a single ovary, embed their seeds in fleshy tissue, and develop a hardened rind. They share growth patterns, pollination strategies, and many of the same genes governing fruit development.
Watermelon’s specific genus is Citrullus, which separates it from cucumbers and melons (genus Cucumis) and from squashes and pumpkins (genus Cucurbita). The genera diverged millions of years ago, but the basic pepo fruit structure has been conserved across all of them, suggesting that it is a deeply successful evolutionary strategy for the family.
What Happens Inside a Ripening Watermelon
The flesh of a watermelon is not just water and sugar, though it is roughly 90 percent water. The red or pink color comes from carotenoid pigments, primarily lycopene, which is the same compound responsible for the red in tomatoes. During ripening, total carotenoid levels climb steadily, reaching around 55 micrograms per gram of fresh weight in fully ripe red-fleshed fruit, with trans-lycopene driving most of that increase.4PubMed Central. Comparative genomics reveals candidate carotenoid pathway regulators of ripening watermelon fruit The mechanism behind all that lycopene accumulation is straightforward: the genes that would normally convert lycopene into other pigments get dialed down as the fruit matures. In red and pink varieties, the enzymes that cycle lycopene into downstream carotenoids show reduced activity around 30 days after pollination, right when lycopene levels start to spike.5Scientia Horticulturae. Expression of carotenogenic genes during the development and ripening of watermelon fruit
The texture of the flesh is another story. Watermelon’s characteristic crispness is tied to cell structure. Firmness correlates strongly with how densely packed the cells are in the flesh. Smaller, more tightly packed cells produce firmer fruit, while larger, more loosely arranged cells yield a softer, mushier bite.6Food Chemistry. Biochemical and histological contributions to textural changes in watermelon fruit modulated by grafting The cell walls themselves matter too: watermelon flesh that has more water-insoluble pectin in its cell walls tends to be firmer. Grafting watermelons onto different rootstocks can actually shift these properties, producing fruit with noticeably different textures from genetically identical scions. It is one of those cases where the berry’s internal anatomy is quietly more complex than it appears when you are just eating a slice.
From Bitter Wild Fruit to Sweet Dessert Berry
The watermelons we eat today bear little resemblance to their wild ancestors. Wild watermelons produce fruit that is watery but typically hard-textured, pale, and bland or outright bitter.7PubMed Central. Origin and emergence of the sweet dessert watermelon, Citrullus lanatus The familiar sweet, red, tender-fleshed watermelon that we recognize appears to have originated from a relatively narrow genetic base, meaning it likely arose through a focused series of human selection events within a single ancestral population rather than from multiple independent domestication efforts.
Genomic research has helped fill in the story. A key stepping stone in watermelon domestication appears to have been the Kordofan melon, a semi-wild form found in Sudan. Genome-level comparisons show that the genetic signature of bitterness loss is already present in the Kordofan melon, but the red flesh color only became fixed in fully domesticated watermelon lines.8PubMed Central. A chromosome-level genome of a Kordofan melon illuminates the origin of domesticated watermelons Bitterness went first, sweetness came gradually. Researchers identified over 15,000 structural differences between the Kordofan melon genome and a modern cultivar, and by tracking those variants across more than 400 watermelon accessions, they found evidence that alleles associated with fruit sweetness shifted in frequency over the long arc of domestication. In other words, sweetness was not a single mutation that flipped a switch. It accumulated, bit by bit, over generations of farmers choosing the tastiest fruits for their seeds.
This domestication history has an interesting implication for the “is it a berry?” question. The basic pepo structure has been there all along, from the bitter wild ancestor to the modern supermarket fruit. Humans did not change the fundamental fruit type. They changed the flavor, the color, and the texture within the existing berry framework. A wild Citrullus fruit picked in the Kalahari ten thousand years ago was just as much a berry as the Sugar Baby you buy in July.
Why No One Calls Them Berries at the Grocery Store
The gulf between botanical classification and everyday language is not a bug in the system. It reflects the fact that the two vocabularies evolved to do different jobs. Botanical terms classify fruits by their developmental origin: which tissue became the edible part, how many ovaries were involved, whether seeds are enclosed in a stone. Culinary terms classify them by how they taste and how people eat them. In culinary usage, “fruits” are the pulpy, seed-bearing plant tissues that taste sweet or tart and are eaten as snacks, desserts, or sweet accompaniments to meals, while “vegetables” are the stems, roots, leaves, and other plant parts typically served in savory dishes.9Journal of Food Composition and Analysis. Classification of fruits and vegetables
By that culinary logic, watermelon is a fruit, not a vegetable, because of its sweetness and the way it is eaten. But nobody at a picnic calls it a berry, because “berry” in everyday English implies something small enough to eat by the handful. The word has social and culinary baggage that has nothing to do with ovary walls and pericarp layers. Both usages are internally consistent. They just serve different communities with different needs.
This split causes more confusion than you might expect, and not just at dinner parties. Nutritional databases, agricultural trade classifications, and food-labeling regulations all have to pick a system, and they do not always agree with one another. The U.S. Supreme Court famously ruled in 1893 that tomatoes are vegetables for tariff purposes, while botanists had been classifying them as berries for centuries. Watermelon does not face quite the same identity crisis since most people accept it as a fruit, but its status as a berry still catches people off guard precisely because the two naming systems rarely come into direct contact in daily life.
Other Surprising Berries and Non-Berries
Part of what makes the watermelon-as-berry fact so disorienting is the company it keeps. Once you accept the botanical definition, a cascade of reclassifications follows. Bananas are berries: they develop from a single ovary, have seeds (those tiny black specks in commercial cultivars), and their flesh comes entirely from the pericarp. Avocados are berries. Grapes are berries. Kiwifruit, persimmons, and even chili peppers all fit the definition.
Meanwhile, many of the fruits that carry “berry” in their common names fail to qualify. Strawberries, as mentioned, are accessory fruits. Mulberries are multiple fruits formed from the ovaries of many separate flowers fused together. Juniper “berries” are actually modified cones. Boysenberries and loganberries, like their parent species, are aggregate drupes. The pattern is consistent: the common English word “berry” was assigned based on appearance and eating experience, long before anyone worked out the reproductive anatomy of these plants.
This is not just trivia. It reflects a genuine tension in how we name the natural world. Common names encode useful practical information: if something looks, feels, and tastes like a berry, calling it one helps people know what to expect. Scientific names encode evolutionary and developmental relationships: if two fruits share the same developmental pathway, classifying them together helps researchers understand gene expression, disease resistance, and breeding potential. Neither system is wrong, and neither is going away. The watermelon simply lives at the intersection where the two systems disagree most visibly.
Seedless Varieties and the Berry Definition
A reasonable follow-up question is whether seedless watermelons still count as berries. After all, if a berry is supposed to contain seeds embedded in its flesh, what happens when we breed those seeds out? The short answer is that seedless watermelons are still berries. They are produced by crossing a diploid plant with a tetraploid one, yielding triploid offspring whose fruits develop without forming mature, viable seeds. The small white seed coats you sometimes find in seedless watermelon are remnants of ovules that started to develop but never completed the process.
Botanically, the fruit structure has not changed. The flesh still develops from the ovary wall, the rind is still a hardened outer pericarp, and the overall developmental pathway is the same as in seeded varieties. The only difference is that the seeds themselves are aborted. Since the definition of a berry concerns the origin of the fruit tissue rather than the viability of the seeds, seedless watermelons remain pepos and therefore remain berries. Seedless bananas work the same way: commercial bananas are parthenocarpic fruits that develop without fertilization, yet they are still classified as berries because the tissue origin is unchanged.
Watermelon Cultivar Diversity and Rind Variation
Most people picture watermelon as green on the outside and red on the inside, but cultivar diversity is enormous. Flesh colors range from deep red to orange, yellow, and even white, depending on which carotenoid pigments accumulate (or fail to accumulate) during ripening. Rind patterns vary too, from dark solid green to light green with dark stripes. And the anatomical details of the rind differ meaningfully between cultivars. Comparative studies of watermelon pericarp anatomy across cultivars have found marked differences in the thickening of outer mesocarp cells in ripe fruits, which affect how well different varieties hold up during transportation and storage.10Indian Journal of Horticulture. Comparative Study of Pericarp Anatomy and Some Fruit Characters in Five Cultivars of Watermelon
Some cultivars develop rinds with especially thick-walled cells, making the fruit more resistant to cracking during shipping. Others prioritize a higher flesh-to-rind ratio, giving you more edible fruit per kilogram but a more fragile package. The tradeoff between rind toughness and edible yield is one of the central tensions in watermelon breeding, and it maps directly onto the pepo identity of the fruit. The rind is not incidental packaging. It is a defining structural feature of this type of berry, and breeders are constantly tinkering with it.
Yellow-fleshed varieties deserve a special mention. Their flesh color results from the accumulation of different carotenoid profiles: instead of lycopene dominating, other carotenoids like beta-carotene or xanthophylls take center stage. The underlying fruit structure is identical to red-fleshed varieties, so they are just as much a pepo and just as much a berry. The color difference is purely about which branch of the carotenoid pathway is most active during ripening, a matter of gene expression rather than fruit architecture. If you have ever bitten into a yellow watermelon and wondered whether it is the same kind of fruit, the answer is yes, all the way down to the ovary wall.