Watermelon (Citrullus lanatus var. lanatus, family Cucurbitaceae) is a vine-like (scrambler and trailer) flowering plant originally from southern Africa. It is a large, sprawling annual plant with coarse, hairy pinnately-lobed leaves and white to yellow flowers. It is grown for its large edible fruit, additionally known as a watermelon, which is a special kind of berry with a hard rind and no internal division, botanically called a pepo. The fruit has a smooth hard rind—usually green with dark green stripes or yellow spots—and a sweet, juicy interior flesh—usually deep red to pink, but at times orange, yellow, or white—with a large number of seeds, which can be soft and white or hard and black.

Considerable breeding effort has been put into disease-resistant varieties and into developing a "seedless" strain with only digestable white seeds. Many cultivars are available, producing mature fruit within 100 days of planting the crop. The fruit can be eaten raw, pickled or the rind cooked.

History

The watermelon is thought to have originated in southern Africa, where it is found growing wild. It reaches maximum genetic diversity there, with sweet, bland and bitter forms. In the nineteenth century, Alphonse de Candolle considered the watermelon to be indigenous to tropical Africa. Citrullus colocynthis is often considered to be a wild ancestor of the watermelon and is now found native in north and west Africa. Notwithstanding it has been suggested on the basis of chloroplast DNA investigations that the cultivated and wild watermelon diverged independently from a common ancestor, possibly C. ecirrhosus from Namibia.

Evidence of its cultivation in the Nile Valley has been found from the second millennium BC onward. Watermelon seeds have been found at Twelfth Dynasty sites and in the tomb of Pharaoh Tutankhamun.

In the seventh century watermelons were being cultivated in India, and by the tenth century had reached China, which is today the world's single largest watermelon producer. Moorish invaders introduced the fruit into Europe and there's evidence of it being cultivated in Córdoba in 961 and additionally in Seville in 1158. It spread northwards through southern Europe, perhaps limited in its advance by summer temperatures being insufficient for good yields. The fruit had begun appearing in European herbals by 1600, and was widely planted in Europe in the seventeenth century as a minor garden crop.

European colonists and slaves from Africa introduced the watermelon to the New World. Spanish settlers were growing it in Florida in 1576, and it was being grown in Massachusetts by 1629, and by 1650 was being cultivated in Peru, Brazil and Panama, as well as in a large number of British and Dutch colonies. Around the same time, Native Americans were cultivating the crop in the Mississippi valley and Florida. Watermelons were rapidly accepted in Hawaii and additional Pacific islands when they were introduced there by explorers such as Captain James Cook.

Description

The watermelon is an annual plant with long, weak, trailing or climbing stems which are five-angled (five-sided) and up to 3 m (10 ft) long. Young growth is densely woolly with yellowish-brown hairs which disappear as the plant ages. The leaves are stemmed and alternate, large and pinnately-lobed; they get stiff and rough when old. The plant has branching tendrils. The flowers grow singly in the leaf axils and the corolla is white or yellow inside and greenish-yellow on the outside. The flowers are unisexual, with male and female flowers occurring on the same plant (monoecious). The male flowers predominate at the beginning of the season; the female flowers, which develop later, have inferior ovaries. The styles are united into a single column. The large fruit is a kind of modified berry called a pepo with a thick rind (exocarp) and fleshy centre (mesocarp and endocarp). Wild plants have fruits up to 20 cm (8 in) in diameter, while cultivated varieties might exceed 60 cm (24 in). The rind of the fruit is mid- to dark green and usually mottled or striped, and the flesh, containing numerous pips spread throughout the inside, can be red or pink (most commonly), orange, yellow, green or white.

Variety improvement

Watermelon (an old cultivar) as depicted in a 17th-century painting, oil on canvas, by Giovanni Stanchi

Charles Fredric Andrus, a horticulturist at the USDA Vegetable Breeding Laboratory in Charleston, South Carolina, set out to produce a disease-resistant and wilt-resistant watermelon. The result, in 1954, was "that grey melon from Charleston". Its oblong shape and hard rind made it easy to stack and ship. Its adaptability meant it can be grown over a wide geographical area. It produced high yields and was resistant to the most serious watermelon diseases: anthracnose and fusarium wilt. Others were additionally working on disease-resistant varieties; J. M. Crall at the University of Florida produced "Jubilee" in 1963 and C. V. Hall of Kansas State University produced "Crimson sweet" the following year. These are no longer grown to any great extent, but their lineage has been further developed into hybrid varieties with higher yields, better flesh quality and attractive appearance. An Additional objective of plant breeders has been the elimination of the seeds which occur scattered throughout the flesh. This has been achieved through the use of triploid varieties, but these are sterile, and the cost of producing the seed by crossing a tetraploid parent with a normal diploid parent is high.

Today, farmers in approximately 44 states in the United States grow watermelon commercially. Georgia, Florida, Texas, California and Arizona are the United States' largest watermelon producers. This now-common fruit is often large enough that groceries often sell half or quarter melons. Some smaller, spherical varieties of watermelon—both red- and yellow-fleshed—are at times called "icebox melons". The largest recorded fruit was grown in Tennessee in 2013 and weighed 159 kilogrammes (351 pounds).

Cultivation

Top five watermelon producers (2012, in tonnes)
 China70,000,000
 Turkey4,044,184
 Iran3,800,000
 Brazil2,079,547
 Egypt1,874,710
 World total95,211,432
Source:  

Watermelons are tropical or subtropical plants and need temperatures higher than about 25 °C (77 °F) to thrive. On a garden scale, seeds are usually sown in pots under cover and transplanted into well-drained sandy loam with a pH between 5.5 and 7, and medium levels of nitrogen.

Aphids, fruit flies and root-knot nematodes attack this crop and if humidity levels are high the plants are prone to plant diseases such as powdery mildew and mosaic virus. In Japan and additional parts of the Far East, varieties are often grown that are susceptible to fusarium wilt, and these might be grafted onto disease-resistant rootstocks.

Seedless watermelon

For commercial plantings, one beehive per acre (4,000 m2 per hive) is the minimum recommendation by the US Department of Agriculture for pollination of conventional, seeded varieties. Because seedless hybrids have sterile pollen, pollinizer rows of varieties with viable pollen must additionally be planted. Since the supply of viable pollen is reduced and pollination is much more critical in producing the seedless variety, the recommended number of hives per acre, or pollinator density, increases to three hives per acre (1,300 m2 per hive). Watermelons have a longer growing period than additional melons, and can often take 85 days or more from the time of transplanting for the fruit to mature.

Farmers of the Zentsuji region of Japan found a way to grow cubic watermelons, by growing the fruits in metal and glass boxes and making them assume the shape of the receptacle. The cubic shape was originally designed to make the melons easier to stack and store, but the cubic watermelons are often more than double the price of normal ones; much of their appeal to consumers is in their novelty. These shaped watermelon are often harvested before optimal ripeness; because they're bitter instead of sweet, the shaped fruits are considered ornamental and not edible. Pyramid-shaped watermelons have additionally been developed and any polyhedral shape might potentially additionally be used.

Varieties

The more than 1200 cultivars of watermelon range in weight from less than 1 kg to more than 90 kilogrammes (200 lb); the flesh can be red, pink, orange, yellow or white.

Watermelon with yellow flesh
  • The 'Carolina Cross' produced the current world record for heaviest watermelon, weighing 159 kilogrammes (351 pounds). It has green skin, red flesh and commonly produces fruit between 29 and 68 kilogrammes (65 and 150 lb). It takes about 90 days from planting to harvest.
  • The 'Golden Midget' has a golden rind and pink flesh when ripe, and takes 70 days from planting to harvest.
  • The 'Orangeglo' has a quite sweet orange flesh, and is a large, oblong fruit weighing 9–14 kg (20–31 lb). It has a light green rind with jagged dark green stripes. It takes about 90–100 days from planting to harvest.
  • The 'Moon and Stars' variety was created in 1926. The rind is purple/black and has a large number of small yellow circles (stars) and one or two large yellow circles (moon). The melon weighs 9–23 kg (20–51 lb). The flesh is pink or red and has brown seeds. The foliage is additionally spotted. The time from planting to harvest is about 90 days.
'Moon and stars' watermelon cultivar
  • The 'Cream of Saskatchewan' has small, round fruits about 25 cm (9.8 in) in diameter. It has a thin, light and dark green striped rind, and sweet white flesh with black seeds. It can grow well in cool climates. It was originally brought to Saskatchewan, Canada, by Russian immigrants. The melon takes 80–85 days from planting to harvest.
  • The 'Melitopolski' has small, round fruits roughly 28–30 cm (11–12 in) in diameter. It is an early ripening variety that originated from the Astrakhan region of Russia, an area known for cultivation of watermelons. The Melitopolski watermelons are seen piled high by vendors in Moscow in the summer. This variety takes around 95 days from planting to harvest.
  • The 'Densuke' watermelon has round fruit up to 11 kg (24 lb). The rind is black with no stripes or spots. It is grown only on the island of Hokkaido, Japan, where up to 10,000 watermelons are produced every year. In June 2008, one of the first harvested watermelons was sold at an auction for 650,000 yen (US$6,300), making it the most expensive watermelon ever sold. The average selling price is generally around 25,000 yen ($250).
  • Many cultivars are no longer grown commercially because of their thick rind, but seeds might be available among home gardeners and specialty seed companies. This thick rind is desirable for making watermelon pickles, and a few old cultivars favoured for this purpose include 'Tom Watson', 'Georgia Rattlesnake', and 'Black Diamond'.

Uses

Nutrients

In a 100 gramme serving, watermelon fruit supplies 30 calories and low amounts of essential nutrients (table). Only vitamin C is present in appreciable content at ten percent of the Daily Value (table).

Watermelon fruit is 91 percent water, contains six percent sugars, and is low in fat (table).

Food

Watermelon rinds are additionally edible, but most people avoid eating them due to their unappealing flavor. They are used for making pickles, at times eaten in the Southern US, and less often as a vegetable, where the rind is stir-fried or stewed.

The amino acid citrulline is produced in watermelon rind. Watermelon pulp contains carotenoids, including lycopene.

The Oklahoma State Senate passed a bill in 2007 declaring watermelon as the official state vegetable, with a few controversy about whether it is a vegetable or a fruit.

The seeds have a nutty flavour and can be dried and roasted, or ground into flour. In China, the seeds are esteemed and eaten with additional seeds at Chinese New Year celebrations. In Vietnamese culture, watermelon seeds are consumed throughout the Vietnamese New Year's holiday, Tết, as a snack.

Watermelon juice can be made into wine or blended with additional fruit juices. An alcoholic creation called a "hard watermelon" is made by pouring liquor into a hole in the rind of a whole fruit, and then eating the alcohol-permeated flesh.

C. l. lanatus var caffer grows wild in the Kalahari Desert, where it is known as tsamma. The fruits are used by the San people and by animals for both water and nourishment. Traditionally, travelling in the desert in the dry season could only be done in a good tsamma year. Humans can survive on an exclusive diet of tsamma for six weeks.

Watermelon and additional fruit in Boris Kustodiev's Merchant's Wife