Prota 2: Vegetables/Lιgumes
Syst. nat. ed. 10(2): 1149 (1759).
2n = 36
Hibiscus sabdariffa L. subsp. cannabinus (L.) G. Panigrahi & Murti (1989).
Kenaf, vegetable kenaf, Guinea hemp, Deccan hemp (En). Kιnaf, chanvre de Guinιe, chanvre de Bombay, da (Fr). Nacacha, nhacandora, cβnhamo brasileiro (Po).
Origin and geographic distribution
Hibiscus cannabinus is a common wild plant in most African countries south of the Sahara. It may have been domesticated as a fibre plant already 6000 years ago in Sudan. Kenaf is now widespread in the tropics and subtropics. As a vegetable it is widely grown in Africa, where it is grown on a much smaller scale as a fibre crop. In the past it has been of some importance as a commercial fibre crop in Cτte dIvoire, Burkina Faso, Togo, Benin, Niger, Kenya, Tanzania and Malawi. India has long been the largest producer of kenaf fibre.
The shoots or young leaves, and sometimes the flowers and young fruits, are used as a vegetable. In Uganda a local delicacy is made from the seeds. These are roasted, ground and pounded, and the flour and skin are separated in water. The flour is rejected but the floating skin parts are used for the preparation of a paste, mixed with boiled pigeon peas. Children chew the bark for its sweetness.
The stem is a source of fibre used in the manufacture of twine, rope and coarse textiles for sacking and cloth for packaging; special fibre cultivars exist. The production of kenaf fibre in Africa is rather uncommon, but locally important, e.g. in northern Nigeria, Niger and Sudan, where it is used for cordage, twines, fishlines and nets. Dried scraped ribbons are used for twine and cordage for sleeping mats. Ribbons and whole stems are a raw material for the pulp and paper industry. Seeds from the fibre crop are used for oil extraction, the rest being used as feed. The oil is suitable as a lubricant and for illumination, for manufacture of soap, linoleum and in paints and varnishes.
In local medicine in Kenya, pounded roots are administered to spider bites, and leaves are used to treat stomach disorders. In West Africa, powdered leaves are applied to sores and boils, and a leaf infusion is administered for treating cough. In India, juice from the flowers is taken against biliousness, while the seed are considered stomachic and aphrodisiac. Whole young plants are an excellent fodder for cattle. The stem core (xylem) is used in combination with peat moss (Sphagnum) and fertilizers as a growth medium for plants. Kenaf plants accumulate minerals such as selenium and boron and can be used as a bioremedial tool for removing these metals from contaminated soil. In West Africa the plants are used as boundary markers.
Production and international trade
Kenaf leaves are sold at local markets in West and Central Africa. Statistics on production and trade as a vegetable are not readily available.
World production of kenaf fibres is estimated at 400,000 t/year averaged over 19972001. India is by far the largest producer (230,000 t/year). In Africa, production is limited and practically all kenaf fibre is produced domestically. Industrial production is reported from Nigeria and Sudan.
The composition of kenaf leaves per 100 g edible portion is: water 79.0 g, energy 280 kJ (67 kcal), protein 5.5 g, fat 1.2 g, carbohydrate 12.2 g, fibre 2.3 g, Ca 484 mg, P 18 mg, Fe 12.1 mg, ascorbic acid 75 mg (Leung, W.-T.W., Busson, F. & Jardin, C., 1968). The composition of kenaf leaves is comparable to other dark green leafy vegetables.
Kenaf produces a bast fibre similar to jute, but with a greater tensile strength, somewhat coarser and more brittle. On a dry weight basis the bast fibre content of the stem ranges from 21% in wild accessions up to 36% in modern cultivars. Individual bast fibres are (1.5)23(12) mm long and (7)1525(41) μm in diameter with a cell wall thickness of 49 μm. Paper made from kenaf bast fibre by chemical pulping is stronger than paper from softwood pulp; paper made from whole stems by chemical pulping has strength properties between paper made from chemical pulp from softwood and that made from hardwood; it is comparatively tight and nonporous compared to paper made from wood.
Seeds contain up to 22(26)% oil, with a fatty acid composition of palmitic acid 1420%, stearic acid 37%, oleic acid 2851% and linoleic acid 2346%. The oil has phytotoxic and fungitoxic properties. The presscake contains: moisture 9%, crude protein 32%, oil 8%, crude fibre 8% and practically no antinutritional components.
Adulterations and substitutes
Kenaf leaves in dishes can be replaced by roselle (Hibiscus sabdariffa L.) or other leafy vegetables.
For many purposes, such as packaging and cordage, kenaf, jute (Corchorus capsularis L.), roselle (Hibiscus sabdariffa L.) and congo jute (Urena lobata L.) may be substituted for each other, although kenaf and roselle are coarser and therefore cheaper than jute.
Annual herb, up to 2 m tall in the wild, up to 5 m in cultivars; taproot well developed, with lateral roots spreading horizontally to 1 m and adventitious roots on lowest stem section; stem erect, slender, cylindrical, prickly on wild accessions. Leaves alternate, simple; stipules filiform, 58 mm long, pubescent; petiole 330 cm long; blade 119 cm Χ 0.120 cm, very shallowly to very deeply palmately 37-lobed in lower part of plant, often unlobed in upper part or even bractlike near the apex, base cuneate to cordate, apex acuminate, margins serrate or dentate, upper surface glabrous but with a prominent, 3 mm long nectary at the base of the midrib, lower surface hairy along the veins. Flowers axillary, solitary or sometimes clustered near the apex of the plant, bisexual, 5-merous, 7.510 cm in diameter; pedicel 26 mm long, articulated at the base; epicalyx of 78 linear segments 718 mm long, persistent; calyx campanulate with acuminate to subcaudate lobes 12.5 cm long (up to 3.5 cm in cultivars), persistent, green, bristly and with a characteristic white, woolly, arachnoid tomentum especially near the base and margins, with a prominent nectary gland on each midrib; petals free, usually spreading, twisted clockwise or anticlockwise, obovate, 46 cm Χ 35 cm, outer side stellate-pubescent, usually cream to yellow with red inner base, sometimes blue or purple; stamens numerous, filaments united into a column surrounding the style, 1723 mm long, dark red, with yellow or red anthers; ovary superior, ovoid, villose, 5-celled, style branching into 35, hairy arms 24 mm long, each branch ending in a capitate stigma. Fruit an ovoid, shortly beaked capsule 1220 mm Χ 1115 mm, densely appressed pubescent, 2025(35)-seeded. Seeds reniform to triangular with acute angles, 34 mm Χ 23 mm, grey to brown-black with pale yellowish spots, hilum brown. Seedling with epigeal germination.
Other botanical information
Hibiscus comprises 200300 species, mainly in the tropics and subtropics, many of which are grown as ornamentals. The estimated number of species varies because opinions differ about inclusion or exclusion of several related groups of species in the genus. Kenaf belongs to Hibiscus section Furcaria, a group of about 100 species which have in common a pergamentaceous calyx (rarely fleshy) with 10 strongly prominent veins, 5 running to the apices of the segments and bearing a nectary, and 5 to the sinuses. Interspecific hybridization has been attempted with variable success between Hibiscus cannabinus and other species within the same section, such as Hibiscus sabdariffa L., Hibiscus radiatus Cav., Hibiscus diversifolius Jacq. and Hibiscus acetosella Welw. ex Hiern.
Hibiscus cannabinus can easily be distinguished from the related species Hibiscus sabdariffa by the white, arachnoid tomentum on the calyx. Hibiscus cannabinus is very variable and various subclassifications have been proposed, but none is generally accepted. The vegetable types such as Malakwang grown in Uganda have a bushy form.
Growth and development
In general kenaf is an obligate short-day plant. Flowering is influenced by the time of planting; long days and high temperatures prolong the vegetative growth phase, an advantage for vegetable and fibre crops. Most cultivars remain vegetative until the photoperiod falls below 12.5 hours. In Ghana, day-neutral early maturing varieties exist that take 4556 days from sowing to flowering.
Kenaf is mainly an out-breeding plant, but up to 30% self-pollination occurs. Flowers open before daybreak and begin to close about midday. The flower structure promotes cross-pollination. The pistil is functional when the flower opens, while the stamens are not dehiscing until shortly after sunrise. While the pistil is still functional, the stigmatic lobes hang down, almost touching the unopened anthers. Later in the day, the stigmatic lobes become turgid and soon stand above the anthers, which lose their pollen. Cross-pollination is mainly effected by insects such as bees. Seeds ripen in about 5 weeks after anthesis. In wild and vegetable types the fruit wall bursts and the seeds are spread on the ground, whilst in fibre types the fruits are indehiscent.
Kenaf grows naturally in grassland and as a weed in fields and wasteland. It is grown from sea level up to an altitude of 2700 m but does not do well above 2500 m and does not tolerate frost. It does well at day temperatures between 16°C and 27°C with 500625 mm rainfall distributed over a period of 45 months. Lower temperatures retard plant growth. It does best on well-drained, neutral sandy loams, rich in humus. It does not tolerate waterlogging.
Kenaf responds well to fertilizers and organic manure, but only farmers producing for the market are prepared to invest in this crop. Manure at a rate of 1020 t/ha is preferred, but if it is not available, an initial application of 250 kg/ha compound fertilizer (e.g. NPK 151515) is recommended. An additional application of nitrogen as side dressing of 50 kg/ha is needed after the first cutting, and this can be repeated after every harvest. Ratoon crops can be picked up to five times when adequate fertilizer is provided. Kenaf may be grown alone or intercropped with other plants. In some regions it is semicultivated as a protected weed for use as a vegetable.
Kenaf grown for fibre grows rapidly and requires little weeding after the first month after sowing.
Propagation and planting
Kenaf is usually propagated from seed but may also be propagated through cuttings. Seed yield is 128 g/plant; the 1000-seed weight 2527 g, in wild forms only 912 g. Under ordinary storage conditions at ambient temperatures and humidity, seeds remain viable for about 8 months. The optimum temperature for seed germination is about 35°C. In home gardens or on small plots of vegetable kenaf, seeds are sown two or three at a time, at spacings of 15 cm Χ 15 cm. This system is also used when interplanting with other crops. Commercial farmers may broadcast the seed for a crop that will be uprooted once the stems are 2030 cm long. For ratoon cropping farmers usually sow in rows 30 cm apart. After a first thinning the within-row spacing is 57 cm. Germination of untreated seed takes about 7 days, longer than for most vegetables; for this reason some farmers soak their seed in water for 24 hours prior to sowing, obtaining emergence after 3 days. The latter method can only be used when rain is expected soon after sowing or when irrigation facilities are available.
For fibre production kenaf is broadcast at a seed rate of 1525 kg/ha or drilled at a spacing of 2030 cm between rows and a 510 cm within rows, but somewhat wider to produce fibre for making paper. Broadcast crops require thinning to about 400,000 plants/ha.
Diseases and pests
Diseases and pests of vegetable kenaf are the same as reported for the fibre crop, and most of them are also similar to these of cotton and okra. The main diseases are: foot, stem and collar rot and wilting caused by Phytophthora; Sclerotium rolfsii causing collar rot; powdery mildew caused by Leveillula taurica; Coniella musaiaensis causing leaf spot; Selenosporella species causing root rot and wilting; Rhizoctonia solani causing stem rot and lodging; Pythium deliense causing root rot; Phomopsis species causing stem spot; Verticillium dahliae causing wilting; Fusarium oxysporum causing wilting and necrosis; tobacco necrosis virus (TNV); and hibiscus latent ringspot virus (HLRSV), which is seed transmitted.
The cotton flea beetle Podagrica puncticollis is a notable pest, most serious in the seedling stage. Oxycarenus spp. and Dysdercus superstitiosus are seed infesting bugs. Kenaf is especially susceptible to root-knot nematodes (Meloidogyne spp.) that may reduce growth and yield especially on light-textured soils. Nematodes also predispose affected plants to pathogenic soil fungi. In order to control nematodes, crop rotation is recommended especially with amaranth or a cereal crop, and liberal application of organic fertilizer. Chemical spraying for control of pests and diseases is rarely applied.
Vegetable kenaf takes 34 weeks from emergence to the first harvesting. As a first thinning, plants of about 20 cm are pulled up and marketed with their roots attached. When ratoon cropping is practised, the second harvest is at the 6-week stage, 23 weeks after the thinning round. Cutting is done at a height of 68 cm, leaving 3 leaves and buds for regrowth. Up to 45 harvests may be carried out at 23-week ratooning intervals. After that, the remaining loose leaves are collected for home consumption. In commercially grown broadcast crops whole plants are pulled up when 2030 cm tall and are sold at the market with their roots attached.
The recommended time of harvesting kenaf as a fibre crop for an optimum balance in fibre yield and quality is when about 50% of the plants are flowering. Plants are cut near the ground and tied into loose bundles that are placed upright in the field for 23 days to induce defoliation and drying. Stems are then graded and tied into bundles of about 10 kg and of even stem thickness.
The yield for once-over harvest as a vegetable by uprooting is 2030 t/ha. For ratoon cropping, a total of 60 t/ha is feasible from 5 harvest rounds, depending on soil fertility and moisture. The highest yields are obtained from the second and third cuts.
World yield of kenaf as a fibre crop averages about 1.2 t dry fibre per ha. The potential yield, obtained in experimental fields with improved cultivars, is 35 t dry fibre per ha.
Handling after harvest
Fresh shoots are easily transported and can be kept in good condition for 12 days especially in shade or cool places. Sprinkling with water helps to keep the leaves fresh. Leaves can be preserved by sun-drying. The dried product is broken into small pieces or ground to powder and used in soups.
For fibre production kenaf stems are usually retted in clear and slow-moving water for a period of 1015 days at temperatures above 30°C to liberate the fibres from the bark. Sometimes stems are decorticated (ribboned) and only the ribbons are steeped in water, cutting retting time by half. When retting is complete, the fibres are stripped manually from the stems, washed thoroughly in clean water and dried well in dust- and sand-free conditions. The dried fibres are transported in crude bales of 60150 kg to the spinning mills. Whole stems may also be transported to pulp- and paper-making factories. Kenaf can be pulped by chemical, semi-chemical and mechanical processes. The alkaline sulphite-anthraquinone process is suitable for kenaf bark and whole stems, giving better yield, strength, viscosity and brightness of the pulp than soda and soda-anthraquinone pulping.
Local landraces of vegetable kenaf are presently not at great risk of genetic erosion, but the genetic variability in fibre cultivars is narrow. In Africa no major collections of kenaf have been reported. The Crop Research Institute in Kumasi, Ghana, has a germplasm collection of local cultivars of the vegetable type. In other countries (India, Bangladesh) large collections of kenaf as fibre crop are maintained. The Bangladesh Jute Research Institute (BJRI) at Dhaka, Bangladesh, has been designated as the world germplasm depository for kenaf and maintains a collection of some 920 accessions, including old and new cultivars, landraces, wild and semiwild accessions of kenaf and related species.
Almost no research has been carried out to enhance the genetic potential. The existing landraces are mixtures of genotypes; the available diversity should be studied and selections made from the desirable types. Purple-flowered strains and the purple false roselle (Hibiscus acetosella) are resistant to the main disease of kenaf, root-knot nematodes; hence they are potential sources of desirable genes in breeding programmes.
Breeding of fibre cultivars with high potential yields under suboptimal conditions is urgent as kenaf grown for fibre is being pushed increasingly towards marginal environments. Other breeding objectives are plants without prickly stems and bristly capsules to facilitate harvesting, and resistance to diseases, nematodes and pests.
Kenaf is a high-yielding and increasingly popular vegetable for the city markets. Contrary to the popular roselle (Hibiscus sabdariffa), it can be grown near the equator. At present its main constraint is its sensitivity to nematodes. If this problem can be solved, vegetable kenaf may well face a bright future.
Kenaf fibre is a biodegradable and environment-friendly raw material suitable for many applications, such as woven and non-woven fabrics, geotextiles and semi-rigid and laminated sheets for packaging and panelling. Kenaf stems are an excellent substitute for softwood as raw material for the pulp and paper industry. Prospects for increased kenaf fibre and pulp production are good in view of growing concerns about environmental pollution and dwindling forest resources.
Blundell, M., 1987. Collins guide to wild flowers of East Africa. Collins, London, United Kingdom. 464 pp.
Burkill, H.M., 1997. The useful plants of West Tropical Africa. 2nd Edition. Volume 4, Families MR. Royal Botanic Gardens, Kew, United Kingdom. 969 pp.
Dempsey, J.M., 1975. Fiber crops. University Presses of Florida, Gainesville, United States. 457 pp.
Edmonds, J.M., 1991. The distribution of Hibiscus L. section Furcaria in tropical East Africa. Systematic and Ecogeographic studies on crop genepools 6. IBPGR, Rome, Italy. 60 pp.
Leung, W.-T.W., Busson, F. & Jardin, C., 1968. Food composition table for use in Africa. FAO, Rome, Italy. 306 pp.
Purseglove, J.W., 1968. Tropical Crops. Dicotyledons. Longman, London, United Kingdom. 719 pp.
Schippers, R.R., 2000. African indigenous vegetables. An overview of the cultivated species. Natural Resources Institute/ACP-EU Technical Centre for Agricultural and Rural Cooperation, Chatham, United Kingdom. 214 pp.
Shamsuddin Ahmad & van der Vossen, H.A.M., 2003. Hibiscus cannabinus L. In: Brink, M. & Escobin, R.P. (Editors). Plant Resources of South-East Asia No 17. Fibre plants. Backhuys Publishers, Leiden, Netherlands. pp. 156162.
Wilson, F.D., 1999. Revision of Hibiscus section Furcaria (Malvaceae) in Africa and Asia. Bulletin of the Natural History Museum, Botany Series 29: 4779.
Akpan, G.A., 2000. Cytogenetic characteristics and the breeding system in six Hibiscus species. Theoretical and Applied Genetics 100(2): 315318.
Amankwatia, Y.O., 1981. Reproductive biology of kenaf (Hibiscus cannabinus L.). Conference Proceedings, Accra, Ghana. 86 pp.
Andrews, F.W., 1952. The flowering plants of the Anglo-Egyptian Sudan, Volume 2. Buncle, Arbroath, United Kingdom. 485 pp.
Angelini, L.G., Macchia, M., Ceccarine, L. & Bonari, E., 1998. Screening of kenaf (Hibiscus cannabinus L.) genotypes for low temperature requirements during germination and evaluation of feasibility of seed production in Italy. Field Crops Research 59(1): 7379.
Banuelos, G.S., 1996. Managing high levels of boron and selenium with trace element accumulator crops. Journal of Environmental Science and Health. Part A. Environmental Science and Engineering and Toxic and Hazardous Substance Control 31(5): 11791196.
Carberry, P.S. & Abrecht, D.G., 1990. Germination and elongation of the hypocotyls and radicle of kenaf (Hibiscus cannabinus) in response to temperature. Field Crops Research 24(34): 227240.
Cook, C.G. & Mullin, B.A., 1994. Growth response of kenaf cultivars in root-knot nematode/soil-borne fungi infested soil. Crop Science 34(6): 14551457.
Crane, J.C., Acuna, J.B. & Alanso, R.E., 1946. Effect of plant spacing and time of planting on fiber yield of kenaf, Hibiscus cannabinus L. Journal of the American Society of Agronomy 38(1): 4659.
Eldin, N.S. & Amin, E.M., 1981. Review of research on the pests of kenaf and their control in the Sudan. Beitrage zur tropischen Landwirtschaft und Veterinarmedizin 19(4): 433437.
Foti, S., Garnaccia, P. & Patane, C., 1998. Production of kenaf (Hibiscus cannabinus L.) seed in Sicily. Agricoltura Ricerca 20(178): 6978.
Gutteridge, R.C., 1988. Alley cropping kenaf (Hibiscus cannabinus) with leucaena (Leuceana leucocephala) in south-eastern Queensland, Australia. Australian Journal of Experimental Agriculture 28(4): 481484.
Lind, E.M. & Tallantire, A.C., 1975. Some common flowering plants of Uganda. 2nd Edition. Oxford University Press, Nairobi, Kenya. 257 pp.
Peters, C.R., O'Brien, E.M. & Drummond, R.B., 1992. Edible wild plants of sub-saharan Africa. Royal Botanic Gardens, Kew, United Kingdom. 239 pp.
Pill, W.G., Tilmon, H.D. & Taylor, R.W., 1995. Nitrogen enriched ground kenaf (Hibiscus cannabinus L.) stem core as a component of soilless growth media. Journal of Horticultural Science 70(4): 673681.
Vawdrey, L.L. & Stirling, G.R., 1992. Reaction of kenaf and roselle grown in the Burdekin River irrigation area to root-knot nematodes. Australasian Plant Pathology 21(1): 812.
Wilson, F.D. & Menzel, M.Y., 1964. Kenaf (Hibiscus cannabinus L.), roselle (Hibiscus sabdariffa L.). Economic Botany 18: 8091.
Sources of illustration
Nabakooza, J., 2003. Illustration Hibiscus cannabinus L. Unpublished.
Correct citation of this article:
Bukenya-Ziraba, R., 2004. Hibiscus cannabinus L. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Lιgumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
wild and planted
1, habit of young plant; 2, flowering shoot.
Redrawn and adapted by Achmad Satiri Nurhaman after original drawing by J. Nabakooza (Artist, Makerere University Herbarium)
young fruits of the vegetable type
flowering plant of the vegetable type
newly harvested bundles of the fibre type