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Ipomoea aquatica Forssk.

Family
Convolvulaceae
Chromosome number
2n = 30
Synonyms
Ipomoea reptans Poir. (1814).
Vernacular names
Kangkong, kangkung, water convolvulus, water spinach, swamp spinach, swamp morning glory (En). Kangkong, liseron d’eau, patate aquatique (Fr). Cancon, batata aquática (Po). Mriba wa ziwa (Sw).
Origin and geographic distribution
Ipomoea aquatica is widespread as a swamp weed in all tropical and many subtropical lowland areas. It is a declared aquatic or terrestrial noxious weed in the south-eastern United States. It occurs in nearly all countries of tropical Africa, from Mauritania and Senegal, east to Eritrea and Somalia, and south to South Africa, and also in the Indian Ocean islands. It is a popular cultivated vegetable in South-East Asia and southern China, but is rare in India. It is known as a leafy vegetable in tropical America, where people of Asian origin cultivate it. It is grown on a small scale under protected cultivation in France, the United Kingdom and the Netherlands for Vietnamese, Thai and Indonesian clients. In tropical Africa it is reported as a collected wild vegetable in Benin, DR Congo, Kenya and Tanzania. Asian cultivars are occasionally grown on a small scale for the Asian clientele near big cities. Kangkong can be found in market gardens, e.g. in Côte d’Ivoire and Nigeria.
Uses
Young shoots and leaves of kangkong are collected for use as a leafy vegetable. Often the whole above-ground plant part of cultivated kangkong, including the tender hollow stems, is consumed. Kangkong can be stir-fried, steamed, boiled for a few minutes or lightly fried in oil and eaten in various dishes. It is often mixed with hot peppers and garlic, and prepared with meat or fish. In Asia the leaves are sometimes separated from the stems, and the stems are cooked a bit longer. In Africa only the leaves of wild plants are consumed, the stems are removed. The roots are occasionally eaten. Wild kangkong is often collected as fodder for cattle and pigs.
In Indonesia, kangkong is traditionally given at dinner to young children to make them quiet and help them sleep well. In Asia it is used in traditional medicine. The sap is used as an emetic, purgative and sedative, and flower buds are applied to ringworm. In Sri Lanka kangkong is used to treat diabetes mellitus.
Production and international trade
In South-East Asia and China, many thousands hectares of kangkong are commercially produced. Thailand and some Caribbean countries export kangkong during the winter months to Europe. There are no production or yield data, and there is no international trade from Africa.
Properties
The nutritional composition of raw kangkong per 100 g edible portion is: water 92.5 g, energy 80 kJ (19 kcal), protein 2.6 g, fat 0.2 g, carbohydrate 3.1 g, dietary fibre 2.1 g, Ca 77 mg, Mg 71 mg, P 39 mg, Fe 1.7 mg, Zn 0.2 mg, vitamin A 6300 IU, thiamin 0.03 mg, riboflavin 0.10 mg, niacin 0.90 mg, folate 57 μg, ascorbic acid 55 mg (USDA, 2002). The nutritional value of leaf-blades is higher than that of petioles and stems; unfortunately, sources do not state whether stems and leaves or leaves only were analysed. Accumulation of heavy metals in kangkong has been reported for Asia because the plants often grow in polluted water.
Kangkong showed oral hypoglycaemic activity in tests with diabetic humans and rats; it was shown that an aqueous leaf extract can be as effective as tolbutamide in reducing blood glucose levels.
Description
Annual or perennial herb with smooth, succulent, hollow stems rooting at the nodes. Leaves alternate, simple; stipules absent; petiole 2–25 cm long; blade ovate or triangular to lanceolate or linear, 2.5–15(–25) cm × 0.5–10 cm, truncate to cordate or hastate at base, entire or coarsely toothed. Inflorescence an axillary 1–7-flowered cyme; peduncle up to 14 cm long. Flowers bisexual, regular, 5-merous; sepals free, ovate, up to 12 mm long; corolla funnel-shaped, 4–10 cm long with a narrow tube and limb c. 5 cm wide, purple, pink or white, often with purple centre; stamens inserted near base of corolla tube, unequal, included; ovary superior, 2-celled, style slender, included, stigmas 2, globular. Fruit a globose to ovoid capsule c. 1 cm in diameter, smooth, brown, enclosed by the sepals, 2–4-seeded. Seeds angular to rounded, c. 4 mm long, densely pubescent, black or pale to dark brown. Seedling with epigeal germination; cotyledons horseshoe-shaped.
Other botanical information
Ipomoea comprises about 500 species and occurs mainly in the tropics.
Two types of cultivated kangkong are distinguished in South-East Asia. The traditional one is close to the wild type and has mostly purple flowers. It is propagated by cuttings. It has tough stems and is always harvested by ratooning. This type is being gradually replaced by white-flowering seed-propagated kangkong, usually grown for once-over harvest, but some strongly branching cultivars are also used for ratooning. Many cultivars of the latter type have been selected, e.g. with big or small leaves, pale or dark green stems and leaves, more or less branching, fast emergence and growth, and improved keeping quality or tenderness.
In Africa, leaves of wild Ipomoea eriocarpa R.Br. and Ipomoea obscura (L.) Ker Gawl. are used as a vegetable in a similar way. Leaves of sweet potato (Ipomoea batatas (L.) Lam.) are a popular vegetable in many places, but their taste and tenderness do not match those of kangkong.
Growth and development
Germination rates of local kangkong cultivars are often low (<60%) because of hard-seededness induced by long storage. Reliable seed companies supply improved cultivars with a high (>80%) germination percentage. Below 25ºC kangkong seeds do not germinate well. Plants start developing lateral branches from cotyledonary buds 2–3 weeks after sowing. Thereafter the main axis and both laterals each produce about one leaf every 2–3 days. Cultivars selected for once-over harvest or uprooting have retarded branching or almost no branching. Ratooning of vegetatively propagated plants or wild plants can start about one month after plant establishment. Once-over harvest of direct sown plants takes place 21–30 days after sowing. After 2–5 months, kangkong starts flowering but meanwhile continues to form new leaves and branches. Kangkong is a quantitative short-day plant, early flowering being induced by short days (<12 hours). Flowering is also stimulated by drought. Kangkong is mainly self -pollinated (60–65%), but cross-pollination by bees and butterflies does occur.
Ecology
Wild kangkong is found floating on water or rooting at the stem nodes in marshy or wet soil, often on river banks and as a weed in rice and other crops on wet soils. It occurs from sea -level up to 1500 m altitude. Cultivated kangkong produces optimum yields in the lowland tropics under high temperatures, full sunshine and abundant water. It is rarely grown above 500 m altitude because at temperatures below 25ºC the growth rate is too slow to make it an economic crop. At higher latitudes it is grown as a summer vegetable. Kangkong is adapted to a wide range of soil conditions, but fertile soils with a high level of organic matter are preferred. The optimum pH is 5.3–6.0.
Management
In upland cultivation weeding is seldom needed, except when germination is slow. Daily watering with ample water is necessary. Although kangkong can do well under conditions of moderate soil fertility, it responds well to N fertilizer and the mineral uptake is high. A general fertilizer recommendation includes manure applied before sowing at a rate of up to 30 t/ha, or 10 t/ha supplemented with N 50 kg/ha , P 30 kg/ha and K 40 kg/ha. This is followed by topdressing at three 10-day intervals with N at a rate of 30, 8 and 8 kg/ha, P at 4, 4 and 0 kg/ha and K at 12, 6 and 0 kg/ha. In case of ratooning, which is common in home gardens, additional top dressing is recommended after each cutting. Application of large amounts of nitrogen fertilizer increases yield and leaf/stem ratio, but also the nitrate content, whereas the dry matter content decreases.
In wet cultivation the water level is raised in accordance with the development of the crop, reaching a depth of 15–20 cm. Young plants cannot withstand flooding. Fertilizer application is similar to upland cultivation, also with a top dressing after each cutting. Cultivation is terminated in the event of flowering or serious losses due to diseases, pests or weeds.
Propagation and planting
Kangkong can be grown as an upland crop or in wet cultivation. Cultivation of upland kangkong is most advanced with market growers in South-East Asia and is also applied for market production in Africa, where the seed is imported from Asian seed companies. The 1000-seed weight is 50–60 g. Seed is either broadcast or sown in rows. The seed may be soaked for 12–24 hours in water before sowing. The seed rate is high, 60–100 g per 10 m2 bed (60–100 kg/ha). If necessary, soils are limed before sowing (2500 kg/ha). Final plant densities may range from 0.3–1.7 million plants/ha. A quick and uniform emergence is an important objective of farmers.
Wet or paddy-field cultivation is still much practised in South-East Asia, but is declining because upland kangkong is more productive and has a better market quality. Planting is usually direct by cuttings, but in some places transplanting 6-week -old seedlings raised on nursery beds is used. Cuttings are planted 3–5 cm deep into the mud. Planting densities vary widely from 0.2–1.5 million cuttings per ha. Locally, floating kangkong without root contact with the soil is grown on a commercial scale in ponds and rivers, in integrated systems with fish, pigs and chicken. Cuttings are anchored to a bamboo frame floating in the water and forming a kind of bed.
Diseases and pests
White rust (Albugo ipomoeae-panduratae, often referred to as Albugo candida), common on sweet potato, is the most common disease of kangkong; it causes white patches which diminish the market quality. Heavy white rust infection may start as soon as two weeks after seedling emergence. Damping off of seedlings caused by Pythium sp. may occur, and occasionally Cercospora leaf spot. Owing to the short growing period, diseases and pests cause fewer problems in once-over harvested crops than in ratooned crops. Where ratooning is practised caterpillars of Spodoptera litura and Diacrisia strigatula and aphids may cause serious damage. Chemical control is a general practice, but hazardous because of residues. Root-knot nematodes (Meloidogyne spp.) are reported as occasionally troublesome in ratoon cropping in dry land, but not in wet soils. Upland kangkong harvested by uprooting and sown repeatedly at the same bed without any crop rotation is remarkably free of soilborne diseases, including nematodes, probably because many noxious nematodes are removed with the roots when uprooting.
Harvesting
Harvesting of upland kangkong takes place from 21–30(–45) days after sowing for once-over harvest by uprooting or cutting at ground level. The damaged basal leaves are removed. The stems of the seedlings are big, tender and crisp.
In wet cultivation, harvesting by cutting young shoots starts 1–2 months after planting, and subsequently at regular intervals, or the plants are cut 5–10 cm above ground level every 4–6 weeks. The stems are thinner and more fibrous and tough than in upland kangkong.
Yield
Under upland cultivation, yields per crop range from 7–30 t/ha of fresh produce, depending largely on the cultivation period. A good once-over harvested crop of 3 weeks produces 1.5–2.0 kg/m2. The potential yield of 12 crops per year from the same bed would add up to 240 t/ha of fresh marketable produce. Under wet cultivation, yields are difficult to compare because cultivation periods differ greatly. Annual yields of 25–100 t/ha are reported in South -East Asia. For floating kangkong an annual production of 90 t/ha of fresh produce is reported for Thailand.
Handling after harvest
Shoots of wetland kangkong are tied into bundles and transported to the market. Entire plants of upland kangkong are washed or wetted and sometimes wrapped in plastic to prevent wilting. For long-distance transport and supermarkets in Asia, kangkong bundles are packed in layers of 15 cm in bamboo crates with crushed ice in between. Kangkong harvested from rivers has a longer shelf life because the leaf area of the young shoots is small.
Genetic resources
Ipomoea aquatica is extremely widespread and not in danger of genetic erosion. Germplasm collections are maintained at the Asian Vegetable Research and Development Center (AVRDC) in Taiwan and at national research institutes in South-East Asia.
Breeding
Consumers have specific preferences with regard to the quality of the product, e.g. number of leaves, stem length, percentage of fibre, and taste. East-West Seed Company in Thailand selected superior cultivars from landraces for characters such as tender thick stems, rapid development, and absence of side shoots for once-over harvest. Some popular cultivars for once-over harvest are ‘Yangtze’ with broad leaves and grown year-round, ‘Salween’ with small bamboo-like leaves and suitable for the hot rainy season, and ‘Liao’ with bamboo-like leaves for the dry season; the strongly branching cultivar ‘Chinwin’ is suitable for multiple harvesting. Northern Thailand, Vietnam and southern China produce much kangkong seed, usually mechanically harvested, with yields up to 1000 kg/ha.
Prospects
Upland kangkong is an excellent vegetable, worth promoting in tropical African lowland areas. The introduction of improved Asian cultivars of upland kangkong might be successful especially in areas where sweet potato leaves are traditionally consumed. Locally, conditions are suitable for seed production. Research should focus on the improvement of fertilizer application and non-chemical control of insect damage. Breeding efforts should concentrate on cultivars adapted to specific African environments and resistant to white rust.
Major references
• Cornelis, J., Nugteren, J.A. & Westphal, E., 1985. Kangkong (Ipomoea aquatica Forssk.): an important leaf vegetable in South-East Asia. Review Article. Abstracts on Tropical Agriculture 10(4): 9–21.
• de Hoop, J.S. & Atmadi Saleh, 2002. Kangkong: a commodity becomes valuable. In: Kunz, K. (Editor). Vegetable breeding for market development: East-West Seeds 1982–2002. Bangkok, Thailand. pp. 65–74.
• East West Seed International, undated. Seed Catalogue. [Internet] http://www.eastwestseed.com. Accessed October 2003.
• Edie, H.H. & Ho, B.W.C., 1969. Ipomoea aquatica as a vegetable crop in Hong Kong. Economic Botany 23(1): 32–36.
• Linnemann, A.R., Louwen, J.M., Straver, G.H.M.B. & Westphal, E., 1986. Influence of nitrogen on sown and ratooned upland kangkong (Ipomoea aquatica Forssk.) at two planting densities. Netherlands Journal of Agricultural Science 34: 15–23.
• Maundu, P.M., Ngugi, G.W. & Kabuye, C.H.S., 1999. Traditional food plants of Kenya. Kenya Resource Centre for Indigenous Knowledge (KENRIK), Nairobi, Kenya. 270 pp.
• Palada, M.C. & Chang, L.C., 2003. Suggested cultural practices for kangkong. International cooperators' guide. [Internet] AVRDC, Shanhua, Taiwan. http://www.avrdc.org/LC/indigenous/kangkong.pdf. Accessed November 2003.
• USDA, 2002. USDA nutrient database for standard reference, release 15. [Internet] U.S. Department of Agriculture, Beltsville Human Nutrition Research Center, Beltsville Md, United States. http://www.nal.usda.gov/fnic/foodcomp. Accessed June 2003.
• van der Zon, A.P.M. & Grubben, G.J.H., 1976. Les légumes-feuilles spontanés et cultivés du Sud-Dahomey. Communication 65. Département des Recherches Agronomiques, Koninklijk Instituut voor de Tropen, Amsterdam, Netherlands. 111 pp.
• Westphal, E., 1993. Ipomoea aquatica Forsskal. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 181–184.
Other references
• Deroin, T., 2001. Convolvulaceae. Flore de Madagascar et des Comores, familles 133 bis et 171. Muséum National d’Histoire Naturelle, Paris, France. pp. 11–287.
• Gonçalves, M.L., 1987. Convolvulaceae. In: Launert, E. (Editor). Flora Zambesiaca. Volume 8, part 1. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 9–129.
• Malalavidhane, T.S., Wickramasinghe, S.M., Perera, M.S. & Jansz, E.R., 2003. Oral hypoglycaemic activity of Ipomoea aquatica in streptozotocin-induced, diabetic wistar rats and type II diabetics. Phytotherapy Research 17(9): 1098–1100.
• Yamaguchi, M., 1990. Asian vegetables. In: Janick, J. & Simon, J.E. (Editors). Advances in new crops. Timber Press, Portland OR, United States. pp. 387–390.
Sources of illustration
• Westphal, E., 1993. Ipomoea aquatica Forsskal. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 181–184.
Author(s)
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands


Editors
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
O.A. Denton
National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria
Associate Editors
C.-M. Messiaen
Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
R.R. Schippers
De Boeier 7, 3742 GD Baarn, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Illustrator
PROSEA
PROSEA Network Office, Herbarium Bogoriense, P.O. Box 234, Bogor 16122, Indonesia
Photo Editor
E. Boer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Grubben, G.J.H., 2004. Ipomoea aquatica Forssk. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
Distribution Map wild


flowering shoot.
Source: PROSEA



flowering crop


crop ready for harvest


habit of flowering plants


flowering plant


cv. Yangtze ready for harvest