Citrullus lanatus (watermelon)
Watermelon has long been valued for its refreshing fruits, which have also been used as an ingredient in cosmetics.
Watermelons in Botswana (Image: T. Ulian)
Citrullus lanatus (Thunb.) Matsum. & Nakai
watermelon, wild watermelon, sweet melon (English); egusi melon (English, Kenya); pastèque, melon d’eau (French).
Least Concern in South Africa according to IUCN Red List criteria; widespread in cultivation.
Grassland and bushland, often along watercourses.
Food and drink.
Some people experience an allergic reaction on ingestion of watermelon, including swelling of the mouth and throat.
About this species
Watermelon is a member of the cucurbit family (Cucurbitaceae), which includes cucumbers (Cucumis sativus), melons (Cucumis melo, for example), loofahs (Luffa species), and pumpkins and squashes (Cucurbita species).
Citrullus lanatus is widely cultivated for its edible fruits, which are also an important source of water in arid regions of Africa.
It is thought that watermelon was first domesticated in central and southern Africa. Watermelon seeds and leaves have been found in ancient Egyptian tombs, suggesting it was cultivated there more than 5,000 years ago.
Having been cultivated for so long, its origins are unknown, but it is thought that it may have been selected from Citrullus colocynthis (known as ‘bitter colocynth’; a bitter, poisonous perennial) in early African agriculture.
Wild, unselected forms tend to bear bitter fruit, due to the presence of cucurbitacin (a biochemical compound used for defence against herbivores) and hence are normally only fed to cattle.
The generic name Citrullus is the diminutive of Citrus, perhaps referring to the spherical fruit. The specific epithet lanatus (meaning woolly) refers to dense woolly hairs on young parts of the plants, particularly stems.
Anguria citrullus Mill., Citrullus amarus Schrad., Citrullus anguria (Duchesne) H.Hara (see full list here).
Geography & Distribution
Citrullus lanatus (Image: Oliver Whaley)
Citrullus lanatus is thought to be native to Africa. It is found in grassland and bushland, mostly on sandy soils, and often along watercourses or near water, up to 1,785 m above sea level. It flourishes in dry climates and requires only limited rainfall.
Some propose the Kalahari region (Botswana, Namibia and South Africa) as the area of origin, whereas others suggest it is native to northeastern Africa. Citrullus colocynthis, thought by some to be the wild parent, is found in dry areas of North Africa and Asia (eastwards to Afghanistan and Pakistan).
Another closely related Namibian species, C. ecirrhosus, is thought more likely to be the progenitor based on studies of plastid DNA. In the wild in Africa, both sweet and bitter forms exist, and they quickly escape from sites of cultivation everywhere into neglected or abandoned farmlands, where they continue to be harvested.
Watermelon is cultivated in all tropical and subtropical countries, as well as in temperate countries with a continental climate. It is widely naturalised.
Flower of Citrullus lanatus (Image: Oliver Whaley)
Overview: An annual climbing or trailing herb, with hairy stem up to 10 m long. Tendrils divided at the tip into two or three parts. Separate male and female flowers are borne on the same plant.
Leaves: Leaf blades up to about 20 × 20 cm, more or less hairy, usually deeply 3–5-lobed, the central lobe being the largest. The lobes themselves are further divided. Leaf stalks (petioles) up to about 19 cm long, more or less hairy.
Flowers: Solitary, borne in leaf axils. Both male and female flowers are yellow, up to 3 cm in diameter, and borne on pedicels (flower stalks) up to 45 mm long. Flowers are usually pollinated by honey bees.
Fruits: Fruits of wild plants up to about 20 cm in diameter, greenish mottled with darker green. Fruits of cultivated plants up to about 70 × 30 cm, rounded, oval or oblong, with a golden-yellow to dark green skin, the skin being uniform, mottled or striped. Flesh usually red or yellow, sometimes orange, pink or white.
Seeds: Flat, smooth, variable in size and colour (white, tan, brown, black, red, green or mottled).
Watermelon fruits (Image: Steve Evans, licensed under the Creative Commons Attribution 2.0 Generic license).
Fruits – food and drink
Watermelons are cultivated commercially for their refreshing, sweet fruits. Dry conditions are considered to produce the sweetest fruit (high humidity is thought to suppress formation of sugars).
They are mostly consumed as fresh fruit, alone or as part of fruit salads or other desserts. In some African cuisines the fruit and leaves are cooked as a vegetable.
Small, white-fleshed cultivars are used in the production of preserves. Watermelon fruits are made into syrup in Eastern Europe. The rind may be consumed in pickled or candied form. In parts of the former Soviet Union, and elsewhere, watermelon juice is fermented to produce an alcoholic beverage.
Watermelons are collected from the wild for local use, notably as a source of water in the Kalahari region of southern Africa. The flesh comprises about 65% of the whole fruit and contains over 90% water. Watermelon contains carotenes and vitamin C.
Seeds – food, oil, masticatory
Watermelon seeds are used in some traditional African cuisines. They are eaten dry or roasted as a snack food or as an ingredient in soups, in the Middle East, China and other Asian countries. Watermelon seeds are rich in edible oils and protein. They are ground into flour and baked as bread in some parts of India.
Watermelon seeds are sold in West African markets as egusi (a name also used for Cucumeropsis mannii, another member of the cucurbit family). They are chiefly used as a masticatory, but also for medicine, food and oil. They are roasted and ground to a pulp, which is added to soup or made into sauce or porridge. Seed oil is extracted for use in cooking.
Seeds can be roasted and used as a coffee-substitute.
Watermelon fruit pulp, juice and seeds have been used as a diuretic. Fruit pulp has been used as a purgative, particularly that from bitter-forms.
A preparation of watermelon seed has been used to lower blood pressure. Watermelon seeds have been used to expel intestinal worms in Senegal.
Bitter forms of watermelon and the cake left over after expressing the seed oil are used as cattle-feed. The leaves and fruit provide grazing for stock.
Watermelon has been used as an ingredient in sun-lotions and other cosmetics.
Role of watermelons in American popular culture
Although watermelon is native to Africa and did not reach the Americas until the 16th century, it rapidly gained favour and assumed an important role in American popular culture.
Thomas Jefferson, third President of the United States, was an enthusiastic grower of watermelons. American author and humorist Mark Twain wrote in Puddn’head Wilson:
"The true southern watermelon is a boon apart and not to be mentioned with commoner things. It is chief of this world’s luxuries, king by the grace of God over all the fruits of the earth. When one has tasted it, he knows what the angels eat."
Watermelons feature prominently in art, literature, advertising and merchandising, and summer watermelon festivals are held throughout the USA.
Millennium Seed Bank: Seed storage
Citrullus lanatus seeds (Image: RBG Kew)
The Millennium Seed Bank Partnership aims to save plant life worldwide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
See Kew’s Seed Information Database for further information on Citrullus lanatus seeds.
This species at Kew
Watermelon is grown in Kew’s behind-the-scenes Tropical Nursery.
Dried and spirit-preserved specimens of Citrullus lanatus are held in Kew’s Herbarium where they are available to researchers by appointment. The details of some of these specimens can be seen online in Kew’s Herbarium Catalogue.
Specimens of watermelon fruits, seeds and oil are held in Kew’s Economic Botany Collection in the Sir Joseph Banks Building, where they are available to researchers by appointment.
Kew’s Useful Plants Project in Botswana
Kew’s Useful Plants Project in Botswana aims to help conserve plant species that are most beneficial to the wellbeing of local people.
One particularly useful species is watermelon, Citrullus lanatus. An important source of water in the Kalahari region over the dry season, it also provides food and medicines.
Working with inhabitants of Tsetseng and Lerala, the project team has agreed which plants are to be propagated in the community gardens. In both communities, facilities have been put in place for training growers and for propagating the useful species. In addition, a school programme has been developed to involve local children in the project.
References and credits
Burkill, H. M. (1997). The Useful Plants of West Tropical Africa, Volume 4, Families M–R. 2nd Edition. Royal Botanic Gardens, Kew, Richmond, UK.
Jeffrey, C. (1967). Cucurbitaceae. In: Flora of Tropical East Africa, E. Milne-Redhead & R. M. Polhills (eds), Crown Agents, UK.
Mabberley, D. J. (2008). Mabberley’s Plant-book: a Portable Dictionary of Plants, their Classification and Uses. 3rd Edition. Cambridge University Press, Cambridge, UK.
Maynard, D. & Maynard, D. N. (2000). Cucumbers, melons and watermelons. In: The Cambridge World History of Food, ed. K. F. Kiple & K. C. Ornelas, Cambridge University Press, Cambridge, UK.
Raimondo, D. et al. (2009). Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
Vaughan, J. G. & Geissler, C. A. (2009). The New Oxford Book of Food Plants. 2nd Edition. Oxford University Press, Oxford, UK.
Welman, M. (2011). PlantZAfrica – Citrullus lanatus. South African National Biodiversity Insitute, South Africa.
Kew science editors: Emma Tredwell and Iain Darbyshire
Copyediting: Emma Tredwell
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