Watermelons have been cultivated in the Nile valley at least since the start of the second millennium BC.
Citrullus lanatus is a prostrate or climbing annual with several herbaceous, rather firm and stout stems up to 3 m long; the young parts are densely woolly with yellowish to brownish hairs while the older parts become hairless. The leaves are herbaceous but rigid, becoming rough on both sides; 60–200 mm long and 40–150 mm broad, ± ovate in outline, sometimes unlobed and ± entire, but usually deeply 3-lobed with the segments again lobed or doubly lobed; the central lobe is much the largest. The leaf stalks are somewhat hairy and up to 150 mm long. The tendrils are rather robust and usually divided in the upper part.
Male and female flowers occur on the same plant (monoecious) with the flower stalk up to 40 mm long and hairy. The receptacle is up to 4 mm long, broadly campanulate and hairy, the lobes are ± as long as the tube. The corolla is usually ± green or green-veined outside and white to pale or bright yellow inside and up to 30 mm in diameter.
The fruit in the wild form is subglobose, indehiscent and up to 200 mm in diameter; the fruit stalk is up to 50 mm long. The fruits in the cultivated forms are globose to ellipsoid or oblong and up to 600 mm long and 300 mm in diameter. The rind in the ripe fruit is hairless and smooth, hard but not woody. In the wild forms the rind is pale or grey-green, usually mottled with irregular longitudinal bands of dark green or grey-green. In cultivated forms the rind is often concolorous yellowish to pale or dark green, or mottled with darker green, or marbled with a darker shade. The flesh in the wild form and some cultivated forms (citron watermelon) is firm and rather hard, white, green-white or yellowish. In cultivated forms the flesh is somewhat spongy in texture but very juicy and soft, pink to bright red-pink. The seeds are numerous, ± ovate in outline, sometimes bordered; in wild forms they are usually black or dark brown; in cultivated forms they are also white or mottled, mostly 6–12 mm long.
Citrullus lanatus can be recognized by its large fruit which is unique in the Cucurbitaceae of southern Africa and also by the dense yellowish to brownish hairs on the younger plant parts.
Citrullus lanatus is not threatened and its status is described as ‘Least Concern' by Raimondo et al . 2009. This means that the species is not at risk of extinction or under threat.
Distribution and habitat
The genus Citrullus is restricted to Africa and parts of Asia and consists of four species, all diploid (2n=22).
- The poisonous perennial C. colocynthis (L.) Schrad. (Colocynthis vulgaris Schrad.) or colocynth, occurs naturally from North Africa and the Mediterranean to Pakistan and Afghanistan; it is also cultivated for medicinal purposes and rodent control in those parts. (Watt & Breyer-Brandwijk (1962) state that Colocynthis vulgaris 'occurs at the Cape'; this not correct).
- The perennial Citrullus ecirrhosus has no tendrils and is restricted to Namibia and the Richtersveld of the Northern Cape.
- The annual C. rehmii is endemic to Namibia.
- C. lanatus [previously known as Citrullus vulgaris Eckl. & Zeyh. and Colocynthis citrullus (L.) Kuntze] is the most polymorphic species of the genus, with both wild and cultivated taxa. Following Laghetti & Hammer (2007), it comprises three subspecies:
- subsp. vulgaris (Schrad. ex Eckl. & Zeyh.) Fursa with the most common edible cultivars of watermelon;
- subsp. mucosospermus Fursa growing in West Africa with wild, semicultivated and cultivated forms;
- subsp. lanatus that includes the var. caffer (Schrad.) Mansf. ex Fursa (tsamma, karkoer, bitterboela), and the var. citroides (Bailey) Mansf. ex Greb. (citron melon, makataan).
New archaeological records raise the possibility that the present distribution of the var. caffer was much more extensive in the past. Many researchers consider this taxon the ancestor of the cultivated watermelon, while others regard the var. citroides as the ancestor. On the other hand, DNA studies show that C. ecirrhosus could be the ancestor of C. lanatus.
C. lanatus is an old cultigen which is now cultivated and in a semi-wild state in the warmer parts of the whole world, but the subsp. lanatus is truly native, most probably only in the more or less sandy drier areas of southern Africa, chiefly in the Kalahari region. In southern Africa it has been collected in Namibia, Botswana and all provinces of South Africa; it is uncommon in Mpumalanga (especially Kruger National Park), KwaZulu-Natal, the Eastern Cape and Western Cape provinces.
Wild C.lanatus subsp. lanatus var. caffer occurs in two biochemically different forms, both with whitish flesh: one with the bitter elaterinid ( karkoer, bitterboela ) and the other without ( tsamma ).These two forms can only be distinguished by taste; there are degrees of bitterness. Apparently the fruit can also taste sour but still refreshing to eat. Farmers in southern Africa have noticed that the edible tsamma with ‘sweet' flesh but bitter rind, occurs mostly in the Kalahari area of Namibia, Botswana and the Northern Cape, but that the bitter karkoer or bitterboela usually occurs elsewhere, often as a weed in old lands, particularly in the North-West, Free State, Western Cape and southern parts of the Northern Cape. Apparently wild animals, cattle and sheep do eat the bitter fruit; however, there is a form with small fruit and a knobbly rind which is poisonous to sheep. (Letter from Dr W. Kotzé to Prof. A.E. van Wyk, University of Pretoria, 2008).
Both C. colocynthis and C. lanatus are mentioned in the Bible (Moldenke & Moldenke 1952).
Derivation of name and historical aspects
The genus name Citrullus is the diminutive of Citrus and probably refers to the globose fruit. The specific epiphet lanatus refers to the dense woolly hairs on the young parts of the plant.
This annual grows in grassland and bushland, mostly in sandy soils, often along water courses or near water. It has been collected at altitudes of 0–1785 m. In southern Africa the flowering time of C. lanatus is mostly from January to April and the fruiting time mostly from February to May. Dry or rainy years will influence flowering and fruiting.
Uses and cultural aspects of Citrullus lanatus
C. lanatus subsp. lanatus var. citroides : The fruit of this cultigen, known as the citron melon or in southern Africa as the makataan, is larger than the tsamma, also sweet and has a more or less concolorous rind and yellowish flesh. It is a traditional crop with several landraces in many parts of the world, e.g. Africa, the Mediterranean and Asia Minor, and introduced in the United States, Polynesia and Russia. The fruits are mostly used as fodder, but also for the production of citron peel or pectin. This plant also occurs as a weed in many countries.
In southern Africa it has been cultivated since pre-colonial times with other crops such as sorghum and maize. The tender young leaves and fruits are cooked as green vegetables, while the fruit flesh may be cooked as porridge with maize meal. It is also a valuable stock feed, especially in times of drought. The makataan is an old favourite for making jam or preserve. The flesh from just below the rind is cut into squares and used to make what is called makataankonfyt . The fruit of the makataan can also be pickled.
C. lanatus subsp. lanatus var . caffer : The tsamma has a crisp, juicy, almost tasteless white flesh. It consists of more than 90% water and contains Vitamin C, ascorbic acid, some trace elements and very few calories. When the pulp is to be drunk, a hole is cut in one end of the fruit and the middle portion eaten. The remaining pulp is then mashed inside with a stick to a watery mass. The seeds are put aside for further use. The hollowed fruit can be used as a container for cooking or storing berries, etc. The pulp and seeds are prepared in a number of different ways for eating. The fruit minus the rind, is cut into slices for drying in the sun, or for mixing with meat, which is then stewed in a hollowed-out fruit. Roasting the entire fruit under a bed of hot coals in the sand adds a lot more flavour to the flesh. The flesh of the bitter karkoer or bitterboela is not used by humans, but the seeds may still be eaten. In the 19 th century Cape Colony the pickled young fruit of the karkoer was consumed; the fresh fruit pulp was used as a drastic purgative, a cathartic in dropsy and other complaints.
The flat brown seeds have a much higher food value than the flesh and have a nice nutty taste. Significant amounts of vitamin C, minerals, fat, starch and riboflavin have been obtained from them. They can be dried, roasted and eaten as such or ground into flour to make bread. The flour is said to contain saponin and is also used as a detergent. The seed contains a high percentage of oil which is similar to pumpkin seed oil and can be used in cooking. The seed oil has an anthelmintic action which is better than that of pumpkin seed oil.
Up to 40 melons have been recorded on one wild plant; their average mass was 1,3 kg. For some Bushmen and animals in the Kalahari, the melons are/were their only source of water for months in the dry season; it is/was not possible to live permanently in the Kalahari without it. In the old days it was almost impossible to travel in the Kalahari desert except during a good tsamma year. The fruit supplied food and water for oxen and even travellers. A person can survive for six weeks on an exclusive diet of tsamma.
Mature fruits of the cultivated watermelon can be stored for not more than four weeks. Mature fruits of the wild C. lanatus subsp. lanatus can remain intact and fleshy for over a year after abscission from the parent plant and they can be stored underground for long periods. H.B. Lecha and U. Posluszny reported on the ‘Comparative fruit morphology and anatomy in Citrullus lanatus ' at the conference of the South African Association of Botanists in 2001. A layer of wax covers the rind of both forms. However, in the cultivated watermelon, stomata occur on the surface of the rind. In contrast, the stomata in the wild fruit are sunken in depressions on the rind; these sunken stomata facilitate the development of stomatal wax plugs after fruit abscission. It was also found that the bands of sclereids comprising the rind tissue are more extensive, broader and more lignified in the wild watermelon than in the cultivated one.
C. lanatus subsp. mucosospermus : The fruit of this West African taxon is somewhat bitter, but the plant is often cultivated on a large scale mainly as cattle food and for the seed. The fruit pulp is eaten either raw or in soup, depending on the degree of sweetness or bitterness. The seed is sold in markets and used as a masticatory, medicine, food or source of oil for cooking and as an illuminant (it is a good substitute for cottonseed oil).
C. lanatus subsp. vulgaris : Cultivation of the watermelon as a fruit crop, began in ancient Egypt and Asia Minor and spread from there. The cultivars of this popular summer fruit grown today, bear little resemblance to their ancestral African forms. The fruit pulp, fruit juice and seed of the watermelon have all been credited with diuretic properties. A preparation of the seed can lower blood pressure. The juice of the root is said to be able to stop bleeding. In China the seeds are used in soups and snacks, in Eastern Europe excess fruits are made into syrup. The flesh is also an ingredient of sunlotions and other cosmetics.
Growing Citrullus lanatus
This member of the Cucumber and Pumpkin Family is propagated by seed and grows easily. The wild forms are not commercially available and are not discussed in South African horticultural books. The tsamma, karkoer and makataan are rather regarded as curiosities and can only be grown in large gardens in fairly dry areas with enough space for the long prostrate stems.
References and further reading
- Jackson, W.P.U. 1990. Origins and meanings of names of South African plant genera . University of Cape Town.
- Jeffrey, C. 1967. Cucurbitaceae. Flora of tropical east Africa .
- Jeffrey, C. 1978. Cucurbitaceae. Flora zambesiaca 4 .
- Laghetti, G. & Hammer, K. 2007. The Corsican citron melon [ Citrullus lanatus (Thunb.) Matsumura & Nakai subsp. lanatus var. citroides (Bailey) Mansf. ex Greb.] a traditional and neglected crop. Genetic Resources and Crop Evolution 54: 913–916.
- Meeuse, A.D.J. 1962. The Cucurbitaceae of southern Africa. Bothalia 8.
- Mabberley, D.J. 2008. Mabberley's Plant-Book: a portable dictionary of plants, their classification and uses. Cambridge University Press.
- Moldenke, H.N. & Moldenke, A.L. 1952. Plants of the Bible . Chronica Botanica, Waltham, Mass., U.S.A.
- Raimondo, D., Von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. & Manyama, P.A. (eds) 2009. Red list of South African plants 2009. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
- Swart, W.J. 1982. Survival off the veld– 12. Good living the Bushman way. Farmer's Weekly , Dec. 17.
- Van Wyk, B.-E. & Gericke, N. 2000. People's plants . Briza Publications, Pretoria.
- Watt, J.M. & Breyer-Brandwijk, M.G. 1962. The medicinal andpoisonousplants of southern and eastern Africa , edn 2. Livingstone, Edinburgh & London.
National Herbarium, Pretoria
In October 2012 John Fry wrote:
I live in Nothern Kwa Zulu. I have just finished reading an article on Citrullus lanatus, I have found it very interesting and would like to relate some information concerning this fruit. During 1892 my grandfather arrived from England aboard a sailing ship and many folk died on the trip over to South Africa of Scurvy. He smuggled himself aboard a sailing ship and when he was discovered he was set a shore at Port Natal where he was handed over to the British garrison. He was put into the army and served a period of time for his sentence. During this time he came aware, of the wild melons growing in the Tugela valley, according to our records these fruit grew in there thousands in the Tugela valley.He then traded with the locals for these melons and transported them back to Port Natal by ox wagon. The melons were then sold to those with sailing ships for food because of the threat of Scurvy. How he discovered that these melons had vitamin C I do not know. But what I do know that is where he started out on his way to success in this country.His name was the same as mine John Fry .