The Watermelon

What Is a Watermelon?

A watermelon (Citrullus lanatus) is a large fruit — technically a berry called a pepo — with a hard rind and sweet, juicy interior. It is 92% water by weight. It is also one of the oldest cultivated foods in human history.

The wild ancestors of watermelon still grow in the Kalahari Desert of southern Africa. They are small, hard, white-fleshed, and bitter — almost inedible. Archaeological evidence from Libya suggests humans were collecting watermelon seeds as early as 5,000 BCE. But the fruit we recognize today was first domesticated in the Nile Valley, where Egyptians were cultivating it by 2,000 BCE.

Who knew? The earliest depictions of watermelon appear in Egyptian tomb paintings from the 12th Dynasty (~2,000 BCE). Hieroglyphics reference a fruit called beden, which scholars believe to be watermelon. The Egyptians placed watermelons in tombs as provisions for the afterlife.

The Propagation of the Watermelon

From Egypt, watermelon spread east through the Middle East and south through Africa. By the 7th century CE, it was being cultivated in India and China. By the 10th century, it had reached Europe through Moorish Spain — the Spanish word sandía comes from Arabic sindiyyah (from Sindh, the region in modern Pakistan).

Europeans brought watermelon to the Americas with the transatlantic slave trade. The first recorded watermelon harvest in the Americas was in 1576 in Florida, planted by Spanish colonists. By the 1600s, watermelons were being grown by Native Americans as far north as the Mississippi Valley.

Today, China produces over 60% of the world’s watermelons — roughly 80 million tons per year. The United States is the 5th largest producer, with Florida, Texas, Georgia, and California accounting for most of the domestic crop.

The Seedless Revolution

Before the 1990s, every watermelon had black seeds. If you wanted to eat a watermelon, you spit seeds. This was the universal experience for 5,000 years.

Seedless watermelons were first developed in the 1940s by Japanese plant geneticist H. Kihara, who discovered that crossing a diploid watermelon (22 chromosomes) with a tetraploid watermelon (44 chromosomes) produced a triploid hybrid (33 chromosomes). Triploid plants are sterile — they cannot produce viable seeds. They can still grow fruit, but the fruit develops with only soft, white, undeveloped seed coats that are edible and unnoticeable (University of Florida IFAS: Seedless Watermelon History).

Seedless watermelons didn’t reach US markets in significant quantity until the 1990s. Today, over 85% of watermelons sold in the United States are seedless. The iconic black-seeded watermelon has become a rarity.

Varieties

There are over 300 varieties of watermelon in cultivation worldwide. The most common in US supermarkets are:

• Sugar Baby — The classic round, dark-green icebox watermelon. 6-10 pounds. Deep red flesh. Developed in 1955 by growers in Oklahoma and still one of the most popular varieties.
• Crimson Sweet — Large oblong watermelon with light-and-dark striped rind. 15-25 pounds. Sweetest of the common grocery store varieties (Brix scale: 12-14). Developed at Kansas State University in 1963.
• Yellow Crimson — Yellow-fleshed variant of Crimson Sweet. Milder, honey-like flavor. Developed at the University of New Hampshire.
• Moon and Stars — A heirloom variety with dark green rind speckled with yellow spots (the “stars”) and one large yellow spot (the “moon”). Originated in Missouri in the 1920s. Nearly extinct by the 1970s; saved by the Seed Savers Exchange.
• Carolina Cross — The giant variety. World record watermelon (350.5 lbs, 2013) was a Carolina Cross. Grown in Tennessee.

The Chemistry of Refreshment

Watermelon’s refreshing quality is not just about water content. The fruit contains high levels of L-citrulline, an amino acid that the body converts to L-arginine, which dilates blood vessels and improves circulation. This is why watermelon is sometimes called nature’s sports drink. It also contains lycopene — a powerful antioxidant responsible for the red color, at higher concentrations than raw tomatoes.

Buying Guide

How to Pick a Watermelon

The traditional method — thumping watermelon to hear a deep hollow sound — actually works, but it requires experience to calibrate. USDA researchers found that a ripe watermelon resonates at a specific frequency (around 120-140 Hz) when thumped, while an underripe one rings at a higher pitch (USDA ARS). The easier method: look for the field spot — the pale yellow patch on the rind where the watermelon rested on the ground. The deeper and more buttery the yellow, the riper the melon.

Common Mistakes

Refrigerating before cutting. Watermelon stops developing sugar once picked but continues ripening (texture change) at room temperature. Refrigerate only after cutting. A whole watermelon kept at room temperature maintains better flavor for up to a week.

Buying pre-cut during peak season. During July and August, the markup on pre-cut watermelon is 3-4x the whole watermelon price. A whole Sugar Baby ($4-6) yields 10-12 cups of cut fruit. The same amount pre-cut costs $12-18.

Eating only the flesh. Watermelon rind is edible and commonly pickled in Southern cuisine. Watermelon seeds are edible, too — they are roasted and eaten as a snack in many cultures (similar to pumpkin seeds). The only part of a watermelon you shouldn’t eat is the very hard outer rind.

Sources

• USDA: Watermelon Production and Consumption
• National Watermelon Promotion Board
• University of Florida IFAS: Watermelon History
• Smithsonian: A History of Watermelon
• USDA ARS: Watermelon Ripeness Testing