Indigofera tinctoria

Family

Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)

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Chromosome number

2n = 16

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Synonyms

Indigofera sumatrana Gaertn. (1791).

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Vernacular names

Indian indigo, common indigo (En). Indigotier tinctorial, indigotier des Indes (Fr). Anileira dos tintureiros, anileira da India (Po). Mnili, mnyuka (Sw).

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Origin and geographic distribution

The origin of Indigofera tinctoria is not known; it possibly originates from India. Its range has been greatly extended by its cultivation for indigo and subsequent naturalization. It occurs wild or naturalized in most countries of Africa, in Asia from Arabia to South-East Asia and in Australia. In Madagascar it seems to occur wild, while in most other Indian Ocean islands it probably has been introduced and sometimes naturalized. In tropical America it certainly has been introduced. Due to its historical exploitation and cultivation it is now distributed pantropically. The use of indigo extracted from Indigofera species has a long history. Indigo plants and the dyestuff were already mentioned in the oldest Sanskrit records. The blue dye used for textiles of Egyptian mummies may, in some cases, come from an Indigofera species but woad (Isatis tinctoria L.) is another indigo-blue producing plant known to ancient Egyptians. The most ancient archaeological textiles discovered in West Africa, the ‘Tellem textiles’, were found in funeral caves in the Bandiagara cliff in the Dogon area of Mali. Some of them date back to the 11^th or 12^th centuries and already include stripes, checks and tie-and-dye patterns done with indigo from Indigofera or Philenoptera species. An early description of the local extraction process of indigo from an Indigofera species in Guinea was left by the Portuguese explorer André Alvares de Almada in 1566.

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Uses

Leafy twigs of Indigofera tinctoria and some closely related Indigofera species are the main sources of the indigo dye used since very ancient times for dyeing textiles blue. The leaves and twigs do not contain indigo but colourless precursors that must be extracted and processed to produce the indigo dye. Because of its fascinating deep blue colour, its great colour fastness to light and the wide range of colours obtained by combining it with other natural dyes, indigo has been called ‘the king of dyes’. No other dye plants have had such a prominent place in as many civilizations as Indigofera species. In western Africa indigo is by far the most important dye of plant origin. It plays an important role in traditional cultures of many people, whether only wearers of indigo-dyed textiles like the Tuareg in the Sahara and Sahel region (Niger, Mali), or renowned indigo dyers, among which the Soninke (Sarakole) and Wolof in Senegal, the Marka women of the Djenné region in Mali, the Dyula and Baule in Côte d’Ivoire, the Yoruba and Hausa in Nigeria and the Bamoum and Bamileke in Cameroon. This part of the world is a major centre of textile decoration techniques based on the concept of ‘resist-dyeing’ and linked with indigo dyeing: intricate patterns are made on the cloth that will resist being dyed. This is done by tying, sewing or plaiting parts of the cloth or by covering them with starch pastes or wax. The piece of cloth is then plunged into the indigo vat to dye the untreated parts. After the resist threads or pastes have been removed, white patterns on a blue ground appear. Light blue patterns on a blue-black ground are formed if a last indigo bath is given after undoing the resist. In Madagascar too, indigo dyeing is very important, for instance in raffia ikats, beautiful textiles in which the ‘resist’ patterns are formed by tying parts of the warp yarns with thick threads before dyeing them with indigo and putting them onto the weaving loom, which again creates white designs on a blue ground. However, the use of natural indigo is rapidly declining and nowadays, synthetic indigo is almost exclusively used, not only in industrialized processes but also at craft level.
Indigofera tinctoria is useful as green manure, used e.g. in India in coffee plantations and preceding rice, maize, cotton and sugarcane. In traditional rainfed rice cropping systems in the Philippines Indigofera tinctoria is a popular green manure, increasing rice yield while reducing the need to supply expensive nitrogen fertilizer to about half. The residue remaining after indigo extraction is also applied as manure. Another reason to grow Indigofera tinctoria as green manure is because it is a good N catch crop, reducing the amount of fertilizer NO₃ leaching to the groundwater. As fodder Indigofera tinctoria is hardly of value. In Kenya it is sometimes fed to camels and sheep, and goats occasionally eat it, but in India it is considered unpalatable to cattle.
In Cameroon twigs are used as a toothbrush. In traditional medicine leaf extracts (sometimes taken with honey or milk) are used to treat epilepsy, nervous disorders, asthma, bronchitis, fever, complaints of stomach, liver, kidney and spleen, as a rabies prophylactic, and as an ointment for skin diseases, wounds, sores, ulcers and haemorrhoids. A leaf extract is also used to treat burns and sores on cattle and horses. A tincture of the seed is used in India to kill lice. A root preparation is applied in Cameroon to relieve toothache, in Tanzania as a remedy against syphilis, gonorrhoea and kidney stone and in India a watery root paste is applied to worm-infested wounds. In India a root infusion is used as an antidote against snakebites and to treat insect and scorpion stings.

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Production and international trade

Already in antiquity indigo was traded from India to the Mediterranean region, but this became more important during the Middle Ages. Large-scale cultivation of Indigofera started in the 16^th century in India and south-eastern Asia. Later, large plantations were established in Central America and the southern United States. The large-scale export of indigo from Asia to Europe started in about 1600 and had to compete with dye from woad which was cultivated mainly in France, Italy, Germany and Great Britain. By the end of the 17^th century, indigo had almost completely replaced woad. Synthetic indigo, which came into commercial production in 1897, proved catastrophic to the production of natural indigo, and by 1914 only 4% of the total world production was of plant origin. Then followed a period in which synthetic indigo lost some of its importance due to competition from new synthetic dyes, but the ever growing popularity of blue jeans enormously contributed to a revival of interest in indigo. At present, the crop is still cultivated for dye production on a small scale in India and in some parts of Africa, southern Arabia (Yemen), Central America and Indonesia. The most important present-day centre of indigo production from Indigofera is probably the northern part of Karnataka state in India. In India, annual production of Indigofera dye gradually decreased from 3000 t from 600,000 ha in 1890, to 50 t from 4000 ha in the 1950s, to an annual export fluctuating between 2 t and 20 t in the 1990s.

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Properties

Indigofera plants contain the glucoside indican. After soaking the plants in water, enzymic hydrolysis transforms indican into indoxyl and glucose. Indigotin (often also called indigo or indigo-blue) formation results from the grouping of two molecules of indoxyl in the presence of oxygen. Indigotin is insoluble in water, so to dye textiles it must be reduced to a soluble form (colourless ‘leuco’ indigo or indigo-white) by a fermentation process under alkaline conditions or by a chemical reducing agent such as sodium dithionite. Subsequent oxidation by airing of the textile after its removal from the dye bath, results in the regeneration of indigotin and fixation of the blue colour onto the textile. Natural indigo can contain varying proportions of a chemically related red dye called indirubin and of the minor isomeric compounds isoindirubin (red) and isoindigo (brown).
The leaves of Indigofera tinctoria contain per 100 g dry matter approximately: N 5.1 g, P 0.35 g, K 1.4 g, Ca 3.9 g. The ash (4.4 g) contains up to 9.5% soluble potassium salts. The indigo refuse after dye extraction contains approximately: N 1.8 g, P 0.2 g, K 0.25 g.
The traditional use of Indigofera tinctoria against liver problems is supported by research findings. Indigtone, a bioactive fraction obtained by fractionation of a petroleum ether extract of the aerial parts of Indigofera tinctoria, showed significant dose-related hepatoprotective activity against carbon tetrachloride induced liver injury in rats and mice. Alcoholic extracts had a very positive effect on the liver antioxidant defence system during D-galactosamine/endotoxin-induced acute hepatitis in rodents. Methanolic extracts of whole plants showed anti-HIV activity in cell cultures.
Indigofera tinctoria has insecticidal properties and contains 6 rotenoids: deguelin, dehydrodeguelin, rotenol, rotenone, tephrosin and sumatrol. Rotenoid concentrations reported are 0.5% in roots, 0.3% in stems, 0.6% in leaves, 0.3% in fruits and 0.4% in seeds. The contents decrease with increasing age of the plant. Sumatrol and tephrosin were not produced in callus cultures of Indigofera tinctoria. In tests the insecticidal property varied. The toxicity of the rotenoids was greater to larvae of the mosquito Anopheles stephensi than to adults of the pulse beetle Callosobruchus chinensis. Extracts obtained from callus cultures were more effective than those obtained from plant parts. The rotenoids had a LD₅₀ value of about 117 ppm against the crustacean Mesocyclops leuckarti, the carrier of Guinea worm larvae (Dracunculus medinensis) which is present in infected drinking water and causes a dangerous parasitic worm infection in humans. Root extracts of Indigofera tinctoria have a strong nematicidal property against Radopholus similis in bananas.

Adulterations and substitutes

Several other, often unrelated, plant species are sources of indigo dyes. Examples include woad from Europe, Polygonum tinctorium Aiton from China, Korea and Japan, Assam indigo (Strobilanthes cusia (Nees) Kuntze) from Indo-China and Thailand and Marsdenia tinctoria R.Br. from tropical Asia. In West Africa, gara (Philenoptera cyanescens (Schumach. & Thonn.) Roberty) and Gambian indigo (Philenoptera laxiflora (Guill. & Perry) Roberty) are important sources of indigo. They also contain indican and are often combined with indigo from Indigofera species in traditional indigo dyeing processes. Other natural sources of indigo are a mutant of the fungus Schizophyllum commune and the purple snail Hexaplex trunculus, which mostly contains precursors of indigo and only minor proportions of the bromine derivatives of indigo of which the famous Tyrian purple dye of antiquity was composed. The most important substitute of natural indigo, however, is the synthetic industrial product.

Description

Annual to perennial herb or subshrub up to 2 m tall; stem erect, copiously branched, covered with appressed, whitish, 2-branched hairs. Leaves arranged spirally, imparipinnate; stipules narrowly triangular, 1.5–3 mm long; petiole up to 2 cm long, rachis up to 7 cm long; stipels narrowly triangular, up to 0.5 mm long; petiolules c. 1 mm long; leaflets (3–)7–17(–21), elliptical to obovate, up to 23 mm × 12 mm, usually glabrous above, thinly hairy below. Inflorescence a sessile, many-flowered axillary raceme up to 6 cm long but usually much shorter; bracts narrowly triangular, c. 1 mm long, more or less persistent. Flowers bisexual, papilionaceous; pedicel 1–1.5 mm long; calyx c. 1 mm long, the tube about as long as the 5 triangular lobes, white appressed hairy; corolla c. 4 mm long, standard ovate, c. 4 mm × 3.5 mm, whitish with reddish rays, wings with very short claws, pinkish, keel laterally spurred, pink to red; stamens 10, 4–5 mm long, upper one free, the other 9 united into a tube; ovary superior, 1-celled, with long style. Fruit a linear pod 20–35 mm long and c. 2 mm wide and thick, straight or slightly curved, rounded in cross-section, brown when ripe, 7–12-seeded with slight constrictions between the seeds. Seeds shortly oblong, c. 2 mm × 1.5 mm, rhombic in cross-section. Seedling with epigeal germination; cotyledons thick, short-lasting.

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Other botanical information

Indigofera is a very large genus comprising approximately 700 species and is distributed throughout the tropics and subtropics of Africa, Asia and the Americas. Africa and the southern Himalayas are richest in species. Over 300 species have been recorded for tropical Africa.
For indigo production several Indigofera species are used but there are 3 closely related major ones: Indigofera tinctoria, Indigofera arrecta Hochst. ex A.Rich., which originates from tropical Africa but is now distributed pantropically, and Indigofera suffruticosa Mill., originating from tropical America and now locally cultivated elsewhere in the tropics, including Africa and Madagascar but not in tropical East Africa. The origin and identity of Indigofera plants cultivated for dye production is often obscure as a result of introduction, selection and the close affinity of species. Indigofera arrecta is sometimes difficult to separate from Indigofera tinctoria. The latter usually differs in its larger and less numerous leaflets and longer fruits containing more seeds. In East Africa, but not in West Africa, Indigofera arrecta generally occurs at higher altitudes (1000–2000 m) than Indigofera tinctoria (below 1000 m). Indigofera suffruticosa differs from Indigofera tinctoria by its rather straight, short, 10–15 mm long, red-brown pods and shorter (c. 3 mm long) stamens. Intermediate specimens between these 3 species have been found, possibly of hybrid origin. Based on the form of the fruits, 2 varieties are distinguished in Indigofera tinctoria: var. tinctoria has straight or slightly curved pods (not more than 50°), var. arcuata J.B.Gillett has pods curved more than 50°, often semi-circular and sometimes forming a ring.

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Growth and development

Seeds germinate in about 4–5 days. Plants may start to flower 3–4 months after sowing. Like many other leguminous plants, Indigofera tinctoria forms root nodules with nitrogen-fixing capacity with e.g. Rhizobium indigoferae. The total lifespan for dye crops is 2–3 years when grown as a ratoon crop.

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Ecology

Indigofera tinctoria occurs in seasonally flooded grassy fields with scattered trees, and also in roadsides, bush margins, brushwood and secondary forest, and on riverbanks, cultivated grounds and sandy coasts. It occurs at 0–1000(–1250) m altitude, in regions with an annual rainfall of 500–1500(–4100) mm and average annual temperature of 23°C. Too much continuous rain, waterlogging and flooding kill plants; excessive heat and hot winds cause withering.

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Propagation and planting

Propagation is by seed, of which 20–30 kg/ha is needed. The seeds commonly have a hard seed coat (sometimes more than 85%) and soaking overnight in water or scarification with sulphuric acid can improve germination to over 90%. Fields are prepared by hoeing or by one or two ploughings after showers followed by light harrowing before and after broadcast sowing. Sowing in a nursery and transplanting into the field may also be practised.

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Management

The crop normally requires little attention after sowing. Weeding is done when needed. Although Indigofera tinctoria is nitrogen fixing by its root nodules, additional N fertilization is not uncommon.

Diseases and pests

No reports on diseases or pests are available for African countries. In Java Indigofera tinctoria is little susceptible to diseases or pests; in humid conditions lignified plants may be attacked by Corticium salmonicolor. In the Philippines pests include chrysomelid beetles and Cletus spp. in the seedling stage and aphids in the vegetative stage. In southern India extensive wilting and drying of Indigofera tinctoria occurs due to infestation by the psyllid Arytaina punctipennis.

Harvesting

Branches are harvested by cutting 10–20 cm above ground level when the plants are 4–5 months old and have formed a closed stand, usually at the flowering stage. The crop should be harvested promptly because heavy rains or flooding can destroy it in a few hours. In India harvested branches are tied into bundles of about 130 kg and transported to the dye factory. Up to 3 harvests are possible per year when it is grown as a ratoon crop.

Yield

In India the yield of green plant material per harvest is 10–13 t/ha. The dye yield is not known.

Handling after harvest

In small-scale cultivation in Africa, harvested branches are often pounded to a soft pulp and made into balls, which are sold on the market after drying. This is the method described by André Alvares de Almada in 1566 and in all early reports. In large-scale cultivation the branches are put in a water containing tank or pit immediately after harvesting. After some hours of fermentation, during which enzymic hydrolysis leads to the formation of indoxyl, the liquid is transferred to another pit or tank and stirred continuously for several hours to stimulate oxidation of the indoxyl to indigotin. Afterwards, the solution is left to rest and the insoluble indigotin settles down to the bottom as a bluish sludge. The water is drained off, and after the indigotin has been washed to get rid of impurities, it is pressed, dried and usually cut into cubes which can be packed and sold.
To dye textiles, indigotin must be reduced to a soluble form under alkaline conditions. In traditional processes (indigo vats), the reduction of indigotin into soluble indigo-white is achieved through a bacterial fermentation. The reducing bacteria are obtained in the bath by adding vegetable matter such as the crushed indigo balls, or, when indigo powder is used, crushed balls of Philenoptera leaves, or, according to some recipes, molasses, coconut-milk, banana or guava leaves. An alkaline pH of around 8.2 is adequate and is maintained by adding a potash lye prepared from the ashes of different calcinated plants specially selected for this purpose in each region (among the Marka women of Mali the most appreciated species are Adansonia digitata L. (baobab), Anogeissus leiocarpa (DC.) Guill. & Perr., Balanites aegyptiaca (L.) Delile, Bauhinia reticulata DC. and Faidherbia albida (Delile) A.Chev.). Less often, the bath is made alkaline by adding freshly slaked lime. In the industrial process, an alkaline solution of sodium dithionite is used for reducing indigo to indigo-white. This polluting chemical process has now been adopted by most craft dyers. Often a gum (e.g. from Acacia senegal (L.) Willd. or Anogeissus leiocarpa (DC.) Guill. & Perr.) is added to make the coloured textile more durable and wind-proof. After the textile has been dipped into the solution of indigo-white, it turns blue when exposed to the air. Several dips are needed to impart a dark blue colour to the textile and especially to cotton fabrics, each dip followed by exposure to the air for some time. In Africa very often dyeing is followed by calendering, a finishing process that consists of beating indigo powder onto the surface of the cloth using heavy mallets to give the textile an iridescent, metallic shine, like on the Tuaregs’ veils. This finish has both aesthetic and medicinal purposes: since the indigo powder is not fixed durably onto the cloth it discharges onto the skin of the people who wear such cloth and acts as a disinfectant and cicatrising drug. Textiles dyed with indigo are very colour-fast to light and washing, less so to rubbing.

Genetic resources and breeding

Several germplasm collections of Indigofera exist, the largest being maintained at CSIRO, St. Lucia, Queensland, Australia (365 accessions) and CIAT, Cali, Colombia (250 accessions). In Africa, collections are present in Ethiopia (ILRI, Addis Ababa, 60 accessions), Kenya (e.g. National Genebank of Kenya Crop Plant Genetic Resources, Kikuyu, (40 accessions) and in South Africa (Pretoria).

Prospects

In spite of its cultural importance, the use of indigo of vegetable origin has almost disappeared, being replaced by synthetic indigo. In West Africa colourful printed textiles, which have a long history in local fashions, are now the most important type of textiles worn by the majority of people and they are mainly imported from Asia or Europe. In recent years, with worldwide increasing concern for sustainability and the demand from consumers for natural products, there has been a revival of interest in natural indigo. Much research still has to be done to optimise indigo production from the most promising plants. Indigofera tinctoria is an interesting species in Africa because in addition to its potential as a dye producer, it can be useful as a green manure in agriculture and as a medicine in traditional healing. Its medicinal properties also deserve more research.

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Major references

• Balfour-Paul, J., 1998. Indigo. British Museum Press, London, United Kingdom. 264 pp.
• Burkill, H.M., 1995. The useful plants of West Tropical Africa. 2nd Edition. Volume 3, Families J–L. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 857 pp.
• Cardon, D., 2003. Le monde des teintures naturelles. Belin, Paris, France. 586 pp.
• Duke, J.A., 1981. Handbook of legumes of world economic importance. Plenum Press, New York, United States, and London, United Kingdom. 345 pp.
• Gillett, J.B., Polhill, R.M., Verdcourt, B., Schubert, B.G., Milne-Redhead, E., & Brummitt, R.K., 1971. Leguminosae (Parts 3–4), subfamily Papilionoideae (1–2). In: Milne-Redhead, E. & Polhill, R.M. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 1108 pp.
• Green, C.L., 1995. Natural colourants and dyestuffs. Non-wood forest products 4. FAO - Food and Agriculture Organization of the United Nations, Rome, Italy. (6 separately numbered chapters and an appendix; also available on internet http://www.fao.org/ docrep/V8879E/ V8879e00.htm). Accessed December 2007.
• Lemmens, R.H.M.J. & Wessel-Riemens, P.C., 1991. Indigofera L. In: Lemmens, R.H.M.J. & Wulijarni-Soetjipto, N. (Editors). Plant Resources of South-East Asia No 3. Dye and tannin-producing plants. Pudoc, Wageningen, Netherlands. pp. 81–83.
• Oei, L. (Editor), 1985. Indigo, leven in een kleur. Stichting Indigo, Amsterdam, Netherlands. 223 pp.
• Schrire, B.D., 1998. Notes relating to the genus Indigofera (Leguminosae–Papilionoideae) for Flora Zambesiaca 2. Section Indigofera. Kew Bulletin 53: 651–668.

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Other references

• Boser-Sarivaxévanis, R., 1969. Aperçus sur la teinture à l’indigo en Afrique occidentale. Verhandlungen der Naturforschenden Gesellschaft in Basel 80(1): 151–315.
• de Melo, F., 1947. Plantas úteis da África Portuguesa. Agéncia Geral das Colónias, Lisbon, Portugal. 301 pp.
• du Puy, D.J., Labat, J.N., Rabevohitra, R., Villiers, J.-F., Bosser, J. & Moat, J., 2002. The Leguminosae of Madagascar. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 750 pp.
• Garrity, D.P., Bantilan, R.T., Bantillan, C.C., Tin, P. & Mann, R., 1994. Indigofera tinctoria: farmer-proven green manure for rainfed ricelands. In: Ladha, J.K. & Garrity, D.P. (Editors). Green manure production systems for Asian ricelands: selected papers from the international rice research conference. International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines. pp. 67–81.
• Gillett, J.B., 1958. Indigofera (Microcharis) in tropical Africa. Kew Bulletin, Additional Series 1, H.M.S.O., London, United Kingdom. 166 pp.
• Hepper, F.N., 1958. Papilionaceae. In: Keay, R.W.J. (Editor). Flora of West Tropical Africa. Volume 1, part 2. 2nd Edition. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 505–587.
• Kamal, R. & Mangla, M., 1987. Rotenoids from Indigofera tinctoria and their bio-efficacy against cyclops, the carrier of dracunculiasis. Pharmazie 42(5): 356.
• Kamal, R. & Mangla, M., 1993. In vivo and in vitro investigations on rotenoids from Indigofera tinctoria and their bioefficacy against the larvae of Anopheles stephensi and adults of Callosobruchus chinensis. Journal of Biosciences 18(1): 93–101.
• Kavimani, S., Jaykar, B., de Clercq, E., Pannecouque, C., Witvrouw, M. & de Clercq, E., 2000. Studies on anti-HIV activity of Indigofera tinctoria. Hamdard Medicus 43(1): 5–7.
• Leite, S.P., de Medeiros, P.L., da Silva, E.C., de Souza-Maia, M.B., de Menezes-Lima, V.L. & Saul, D.E., 2004. Embryotoxicity in vitro with extract of Indigofera suffruticosa leaves. Reproductive Toxicology 18(5): 701–705.
• Malarvannan, L. & Devaki, T., 2003. Protective effect of Indigofera tinctoria on tissue antioxidant defence system against D-galactosamine and endotoxin-induced hepatopathy in rats. Journal of Natural Remedies 3(1): 49–53.
• Miège, J., 1992. Couleurs, teintures et plantes tinctoriales en Afrique occidentale. Bulletin du Centre Genevois d’Anthropologie 3: 115–131.
• Monteil, C., 1971. Une cité soudanaise. Djenné, métropole du delta central du Niger. Institut International Africain. Editions Anthropos, Paris, France (Reprint of the 1932 edition of the Société d’Editions Géographiques, Maritimes et Coloniales, Paris, France). 311 pp.
• Picton, J. & Mack, J., 1979. African textiles. Looms, weaving and design. British Museum Publications, London, United Kingdom. pp. 37–42.
• Singh, B., Saxena, A.K., Chandan, B.K., Bhardwaj,V., Gupta, V.N., Suri, O.P. & Handa, S.S., 2001. Hepatoprotective activity of indigtone - a bioactive fraction from Indigofera tinctoria Linn. Phytotherapy Research 15(4): 294–297.
• Sreeja, P. & Charles, J.S.K., 1998. Screening of botanicals against the burrowing nematode, Radopholus similis (Cobb. 1893) Thorne, 1949. Pest Management in Horticultural Ecosystems 4(1): 36–39.
• Sreepriya, M., Devaki, T. & Nayeem, M., 2001. Protective effects of Indigofera tinctoria L. against D-galactosamine and carbon tetrachloride challenge on in situ perfused rat liver. Indian Journal of Physiology and Pharmacology 45(4): 428–434.
• Sudibyo Supardi & Hurip Pratomo, 2003. Indigofera L. In: Lemmens, R.H.M.J. & Bunyapraphatsara, N. (Editors). Plant Resources of South-East Asia No 12(3). Medicinal and poisonous plants 3. Backhuys Publishers, Leiden, Netherlands. pp. 261–263.
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Afriref references

Sources of illustration

• Gillett, J.B., Polhill, R.M., Verdcourt, B., Schubert, B.G., Milne-Redhead, E., & Brummitt, R.K., 1971. Leguminosae (Parts 3–4), subfamily Papilionoideae (1–2). In: Milne-Redhead, E. & Polhill, R.M. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 1108 pp.
• Mansfeld, R., 1986. Verzeichnis landwirtschaftlicher und gärtnerischer Kulturpflanzen (ohne Zierpflanzen). 2nd edition, revised by J. Schultze-Motel. 4 volumes. Springer Verlag, Berlin, Germany. 1998 pp.

Author(s)

•	R. Takawira-Nyenya National Herbarium and Botanical Garden, P.O. Box A 889, Avondale, Harare, Zimbabwe
•	D. Cardon CNRS, CIHAM-UMR 5648, 18, quai Claude-Bernard, 69365 Lyon, Cedex 07, France

Editors

•	P.C.M. Jansen PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
•	D. Cardon CNRS, CIHAM-UMR 5648, 18, quai Claude-Bernard, 69365 Lyon, Cedex 07, France

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

Photo editor

•	E. Boer PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article

Takawira-Nyenya, R. & Cardon, D., 2005. Indigofera tinctoria L. [Internet] Record from PROTA4U. Jansen, P.C.M. & Cardon, D. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>. Accessed .

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