Watermelon

The watermelon is an annual that has a prostrate or climbing habit. Stems are up to 3 metres (10 feet) long and new growth has yellow or brown hairs. Leaves are 60 to 200 millimetres (2 ¹⁄₄ to 7 ³⁄₄ inches) long and 40 to 150 mm (1 ¹⁄₂ to 6 in) wide. These usually have three lobes which are themselves lobed or doubly lobed. Plants have both male and female flowers on 40-millimetre-long (1 ¹⁄₂ in) hairy stalks. These are yellow, and greenish on the back.[3]

The watermelon is a large 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 large, coarse, hairy pinnately-lobed and alternate; they get stiff and rough when old. The plant has branching tendrils. The white to yellow 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 center (mesocarp and endocarp).[4] Wild plants have fruits up to 20 cm (8 in) in diameter, while cultivated varieties may 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.[5][6]

A bitter watermelon has become naturalized in semiarid regions of several continents, and is designated as a "pest plant" in parts of Western Australia where they are called "pig melon".[7]

The species has two varieties, watermelons (Citrullus lanatus (Thunb.) var. lanatus) and citron melons (Citrullus lanatus var. citroides (L. H. Bailey) Mansf.), originated with the erroneous synonymization of Citrullus lanatus (Thunb.) Matsum. & Nakai and Citrullus vulgaris Schrad. by L.H. Bailey in 1930.[8] Molecular data including sequences from the original collection of Thunberg and other relevant type material, show that the sweet watermelon (Citrullus vulgaris Schrad.) and the bitter wooly melon Citrullus lanatus (Thunb.) Matsum. & Nakai are not closely related to each other.[9] A proposal to conserve the name, Citrullus lanatus (Thunb.) Matsum. & Nakai, was accepted by the nomenclature committee and confirmed at the International Botanical Congress in 2017.[10]

The sweet watermelon was formally described by Carl Linnaeus in 1753 and given the name Cucurbita citrullus. It was reassigned to the genus Citrullus in 1836, under the replacement name Citrullus vulgaris, by the German botanist Heinrich Adolf Schrader.[11] (The International Code of Nomenclature for algae, fungi, and plants does not allow names like "Citrullus citrullus".)

The bitter wooly melon is the sister species of Citrullus ecirrhosus Cogn. from South African arid regions, while the sweet watermelon is closer to Citrullus mucosospermus (Fursa) Fursa from West Africa and populations from Sudan.[12] The bitter wooly melon was formally described by Carl Peter Thunberg in 1794 and given the name Momordica lanata.[13] It was reassigned to the genus Citrullus in 1916 by Japanese botanists Jinzō Matsumura and Takenoshin Nakai.[14]

Still Life with Watermelons, Pineapple and Other Fruit by Albert Eckhout, a Dutch painter active in 17th-century Brazil

Illustration from the Japanese agricultural encyclopedia Seikei Zusetsu (1804)

The watermelon is a flowering plant that originated in Africa, though there is conflicting research about whether its source is West Africa[15] or Northeast Africa.[16]

Evidence of the cultivation of both C. lanatus and C. colocynthis in the Nile Valley has been found from the second millennium BC onward, and seeds of both species have been found at Twelfth Dynasty sites and in the tomb of Pharaoh Tutankhamun.[17] Watermelons were cultivated for their high water content and were stored to be eaten during dry seasons, not only as a food source, but as a method of storing water.[16] Watermelon seeds were also found in the Dead Sea region at the ancient settlements of Bab edh-Dhra and Tel Arad.[18]

A number of 5000-year old wild watermelon seeds (C. lanatus) were discovered at Uan Muhuggiag, a prehistoric archaeological site located in southwestern Libya. This archaeobotanical discovery may support the possibility that the plant was more widely distributed in the past.[2][16]

In the 7th century, watermelons were being cultivated in India, and by the 10th century had reached China, which is today the world's single largest watermelon producer. The Moors introduced the fruit into the Iberian Peninsula and there is evidence of it being cultivated in Córdoba in 961 and also 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 17th century as a minor garden crop.[5]

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. Around the same time, Native Americans were cultivating the crop in the Mississippi valley and Florida. Watermelons were rapidly accepted in Hawaii and other Pacific islands when they were introduced there by explorers such as Captain James Cook.[5] In the Civil War era United States, watermelons were commonly grown by free black people and became one symbol for the abolition of slavery.[19] After the Civil War, black people were maligned for their association with watermelon. The sentiment evolved into a racist stereotype where black people shared a supposed voracious appetite for watermelon, a fruit long correlated with laziness and uncleanliness.[20]

Seedless watermelons were initially developed in 1939 by Japanese scientists who were able to create seedless triploid hybrids which remained rare initially because they did not have sufficient disease resistance.[21] Seedless watermelons became more popular in the 21st century, rising to nearly 85% of total watermelon sales in the United States in 2014.[22]

Watermelons are plants grown in climates from tropical to temperate, needing 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.

Major pests of the watermelon include aphids, fruit flies, and root-knot nematodes. In conditions of high humidity, the plants are prone to plant diseases such as powdery mildew and mosaic virus.[23] Some varieties often grown in Japan and other parts of the Far East are susceptible to fusarium wilt. Grafting such varieties onto disease-resistant rootstocks offers protection.[5]

Seedless watermelon

The US Department of Agriculture recommends using at least one beehive per acre (4,000 m² per hive) for pollination of conventional, seeded varieties for commercial plantings. Seedless hybrids have sterile pollen. This requires planting pollinizer rows of varieties with viable pollen. 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 (pollinator density) increases to three hives per acre (1,300 m² per hive). Watermelons have a longer growing period than other melons, and can often take 85 days or more from the time of transplanting for the fruit to mature.[24] Lack of pollen is thought to contribute to "hollow heart" which causes the flesh of the watermelon to develop a large hole, sometimes in an intricate, symmetric shape. Watermelons suffering from hollow heart are safe to consume.[25][26]

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.[27] The cubic shape was originally designed to make the melons easier to stack and store, but these "square watermelons" may be triple the price of normal ones, so appeal mainly to wealthy urban consumers.[27] Pyramid-shaped watermelons have also been developed and any polyhedral shape may potentially be used.[28]

A number of cultivar groups have been identified:[29]

Varieties

The more than 1,200[31] cultivars of watermelon range in weight from less than 1 kilogram (2 ¹⁄₄ pounds) to more than 90 kg (200 lb); the flesh can be red, pink, orange, yellow or white.[24]

• The 'Carolina Cross' produced the current world record for heaviest watermelon, weighing 159 kg (351 lb).[32] It has green skin, red flesh and commonly produces fruit between 29 and 68 kg (65 and 150 lb). It takes about 90 days from planting to harvest.[33]
• The 'Golden Midget' has a golden rind and pink flesh when ripe, and takes 70 days from planting to harvest.[34]
• The 'Orangeglo' has a very 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.[35]
• The 'Moon and Stars' variety was created in 1926.[36] The rind is purple/black and has many small yellow circles (stars) and one or two large yellow circles (moon). The melon weighs 9–23 kg (20–51 lb).[37] The flesh is pink or red and has brown seeds. The foliage is also spotted. The time from planting to harvest is about 90 days.[38]
• The 'Cream of Saskatchewan' has small, round fruits about 25 cm (10 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.[39]
• 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.[40]
• 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).[41]
• Many cultivars are no longer grown commercially because of their thick rind, but seeds may be available among home gardeners and specialty seed companies. This thick rind is desirable for making watermelon pickles, and some old cultivars favoured for this purpose include 'Tom Watson', 'Georgia Rattlesnake', and 'Black Diamond'.[42]

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

Variety improvement

Charles Fredrick 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 gray melon from Charleston". Its oblong shape and hard rind made it easy to stack and ship. Its adaptability meant it could be grown over a wide geographical area. It produced high yields and was resistant to the most serious watermelon diseases: anthracnose and fusarium wilt.[43]

Others were also working on disease-resistant cultivars; 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.[5] Another 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.[5]

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, with Florida producing more watermelon than any other state.[44] 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 sometimes called "icebox melons".[45] The largest recorded fruit was grown in Tennessee in 2013 and weighed 159 kilograms (351 pounds).[32]

Watermelon production, 2017 (millions of tonnes)
China	79.3
Iran	4.0
Turkey	3.9
Brazil	2.3
World	118.4
Source: FAOSTAT of the United Nations[46]

In 2017, global production of watermelons was 118 million tonnes, with China alone accounting for 67% of the total.[46] Secondary producers included Iran, Turkey, and Brazil.[46]

Watermelon is a sweet, commonly consumed fruit of summer, usually as fresh slices, diced in mixed fruit salads, or as juice.[47][48] Watermelon juice can be blended with other fruit juices or made into wine.[49]

The seeds have a nutty flavor and can be dried and roasted, or ground into flour.[6] In China, the seeds are eaten at Chinese New Year celebrations.[50] In Vietnamese culture, watermelon seeds are consumed during the Vietnamese New Year's holiday, Tết, as a snack.[51]

Watermelon rinds may be eaten, but their unappealing flavor may be overcome by pickling,[42] sometimes eaten as a vegetable, stir-fried or stewed.[6][52]

The Oklahoma State Senate passed a bill in 2007 declaring watermelon as the official state vegetable, with some controversy about whether it is a vegetable or a fruit.[53]

Citrullis lanatus, variety caffer, grows wild in the Kalahari Desert, where it is known as tsamma.[6] The fruits are used by the San people and wild animals for both water and nourishment, allowing survival on a diet of tsamma for six weeks.[6]

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  Watermelon cubes
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  Watermelons with dark green rind, India
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  Watermelon flowers
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  Watermelon leaf
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  Flower stems of male and female watermelon blossoms, showing ovary on the female
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  Watermelon plant close-up
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  Watermelon baller
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  Watermelon with yellow flesh
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  'Moon and stars' watermelon cultivar
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  Watermelon and other fruit in Boris Kustodiev's Merchant's Wife
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  Watermelon for sale
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  Watermelon out for sale in Maa Kochilei Market, Rasulgarh, Odisha, India
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  Watermelon grown in Buryatia, Siberia
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  Watermelon rind curry
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  Roasted and salted watermelon seeds
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  Watermelon seed under a microscope

• List of fruits

Wikispecies has information related to Citrullus vulgaris.

Wikimedia Commons has media related to Citrullus lanatus.

• Watermelon.org from the US National Watermelon Promotion Board