Indigofera (PROSEA Dyes and tannins)
- Protologue: Sp. Pl. 2: 751 (1753); Gen. Pl. (ed. 5): 333 (1754).
- Family: Leguminosae
- Chromosome number: x= 8; 2n= 16: I. arrecta, I. suffruticosa, I. tinctoria
Major species and synonyms
- Indigofera arrecta Hochst. ex A. Rich., Tent. Fl. Abys. 1: 184 (1847);
- Indigofera suffruticosa Miller ssp. suffruticosa , Gard. Dict. ed. 8, No 2 (1768), synonym: I. anil L. (1771);
- Indigofera suffruticosa Miller ssp. guatemalensis (Mocino, Sessé & Cerv. ex Backer) de Kort & Thijsse, Blumea 30: 135 (1984), synonym: I. guatemalensis Mocino, Sessé & Cerv. ex Backer (1908);
- Indigofera tinctoria L., Sp. Pl. 2: 751 (1753), synonym: I. sumatrana Gaertner (1791).
- indigo (En)
- Indonesia: tom, tarum
- Malaysia: tarom
- Philippines: anil
- Thailand: khram
- Vietnam: châm.
I. arrecta :
- Natal-indigo, Bengal-indigo, Java-indigo (En)
- Indonesia: tom atal, tom katemas (Javanese).
I. suffruticosa ssp. suffruticosa :
- Indonesia: taem-taem, tagom-tagom, tom cantik
- Philippines: tina-tinaan (Tagalog), tayum (Bisaya, Ilokano)
- Thailand: khraam-thuean (Shan-Chiang Mai), khraam yai (Ubon Ratchathani).
I. suffruticosa ssp. guatemalensis :
- Guatemala-indigo (En)
- Indonesia: tom presi.
I. tinctoria :
- Common indigo, Indian indigo (En)
- Indonesia: tom jawa, tarum alus, tarum kaju
- Malaysia: nila, tarum
- Philippines: tagung-tagung (Bisaya), taiom (Ilokano), taiung (Pampango)
- Cambodia: trôm
- Laos: khaam
- Thailand: khraam (general), na-kho (Karen, Mae Hong Son)
- Vietnam: chàm, chàm nhuôm.
Origin and geographic distribution
The large genus Indigofera (ca. 700 spp.) is distributed throughout the tropics and subtropics of Asia, Africa and the Americas; most of the species occur in Africa and the southern Himalayas. About 40 species are native to South-East Asia, and many others have been introduced. Many species are cultivated in all tropical regions. I. arrecta is a native of East and southern Africa and has been introduced in Laos, Vietnam, the Philippines (Luzon) and Indonesia (Sumatra, Java, Sumba, Flores). Both the subspecies of I. suffruticosa originate from tropical America, and are locally cultivated in Java. I. tinctoria probably originates from Asia, but its distribution is now pantropical.
Indigofera species are widely used as a source of the blue dye indigo throughout the tropics. They are also recommended as a cover crop and for green manure, especially in tea, coffee and rubber plantations. The leaves of I. arrecta and I. tinctoria are used in traditional medicines for epilepsy and nervous disorders and to heal sores and ulcers.
Production and international trade
The cultivation of Indigofera on a large scale started in the 16th Century in India and South-East Asia. Later large plantations were also established in Central America and the southern United States. The export of indigo to Europe was of great importance and had to compete with the dye from woad, Isatis tinctoria L., which was cultivated mainly in France, Germany and Great Britain. The commercial production of synthetic indigo, which came into use in 1897, proved catastrophic to the production of natural indigo, and by 1914 only 4% of the total world production was of vegetable origin. At present, the crop is still cultivated for dye on a small scale in India (in the northern part of Karnataka) and in some parts of Africa and Central America. In Indonesia, Indigofera is still grown in some villages on the north coast of Java and in the whole of east Indonesia where natural indigo is used for traditional and ritual fabrics.
Indigofera plants contain the glucoside indican. After soaking the plants in water, enzymic hydrolysis transforms indican into indoxyl (indigo-white) and glucose. Indoxyl can be oxidized to indigo-blue.
Many species contain toxic organic nitro compounds. However, I. tinctoria is said to be palatable to cattle.
The leaves of I. arrecta and I. tinctoria contain respectively (% dry matter basis): N 4.46, 5.11; P2O5 0.02, 0.78; K2O 1.95, 1.67; CaO 4.48, 5.35.
The genus Indigofera comprises shrubs, shrublets and herbs (but then woody at the base), with spreading or ascending branches and with indumentum of biramous hairs. Leaves alternate, usually imparipinnate, sometimes trifoliolate or unifoliolate. Flowers in axillary racemes, pedicelled, calyx campanulate with 5 teeth, corolla papilionaceous. Fruit generally a linear pod (in some species almost globose), straight or upcurved, with 1-20 mostly globose to ellipsoid seeds. Seedlings with epigeal germination, cotyledons thick, short-lasting.
I. arrecta is a large shrub up to 3 m tall, often cultivated as an annual, with ca. 5 mm long flowers and 2-2.5 cm long straight pods, containing 6-8 seeds.
I. suffruticosa ssp. suffruticosa is a shrub up to 2.5 m tall with 5 mm long flowers and curved pods, containing 4-6 seeds.
I. suffruticosa ssp. guatemalensis has smaller flowers (3 mm) and straight pods with 1-3 seeds.
I. tinctoria is a small shrub (up to 1 m tall) with 5 mm long flowers, straight or slightly curved pods, containing 7-12 seeds.
Other botanical information
I. arrecta, I. suffruticosa and I. tinctoria are closely related and intermediate specimens (possibly of hybrid origin) have been found.
In India, Indigofera articulata Gouan has also been cultivated as a dye-producing plant. However, it has never been introduced for dyeing in South-East Asia.
Indigofera species can be grown from sea-level up to 1650 m and do best on permeable soils, rich in organic matter. As a dye plant Indigofera is grown on upland soils and as a secondary crop on paddy soils. Land should be properly drained.
When used as a cover crop, I. arrecta can only be grown in gardens with little or no shade. Plants prefer a hot, moist climate with a rainfall of no less than 1750 mm/year. The crop withstands waterlogging for up to 2 months.
I. tinctoria does not tolerate heavy rainfall and waterlogging.
In the natural or naturalized state, species are found on open, sunny places such as wasteland, road-sides, riverbanks and grassland, sometimes up to 2000 m above sea-level.
Propagation and planting
Propagation is by seed, except for I. suffruticosa, which is propagated by cuttings. To prevent insect damage seeds can be treated with wood ash before sowing. Seeds of I. arrecta possess a hard seed-coat and must be scarified. Land is prepared by ploughing or by hoeing. Sowing is done either on seed-beds or directly into the field, 3-4 seeds per hole, 60 cm apart within rows and 45-60 cm between rows. Germination takes about 4 days. When seed-beds are used, seedlings are transplanted at 4-6 weeks.
Cuttings are made by dividing well-developed branches into pieces 30 cm long, which are kept for 2-3 days in a cool place before planting.
Cuttings, 2-3 per hole, start rooting by the second week.
Weeding and earthing up is done about 1 month after planting and again 1 month later. Cover crops are slashed at regular intervals.
Diseases and pests
I. arrecta can be attacked by Bacillus solanacearum. On Java I. tinctoria is not susceptible to pests and diseases; after lignification, however, in humid regions, it is attacked by Corticium salmonicolor (jamur upas). In other production areas I. tinctoria is reported to be attacked by various fungi and insects and by the nematode Heterodera glycines.
Branches are harvested, usually early in the morning, when the plants are 4-5 months old and the crop has made a closed stand. This is usually the flowering stage. About 3-4 months later the plants can be cut again; a crop can be harvested three times a year. The total life span for dye crops is 2-3 years, and 1.5-2 years for cover crops. Indigo is harvested only once on paddy soils because the plants must give way for the next rice crop.
I. arrecta is the chief source of blue dye; it is also used as a cover crop and a green manure crop. The yield from this species is higher than from any other species of Indigofera. Annual yields of 22-100 t green matter per ha have been reported in India; the recorded output of indigo cake is 137-325 kg/ha per year.
Yields of I. tinctoria as a dye crop are in the order of 10-13 t/ha of green matter per year, but may vary widely according to area, season and cultivation method.
Handling after harvest
The harvested branches are placed in a tank containing water to which some lime has been added and weighted down with planks. After some hours of fermentation, during which enzymic hydrolysis leads to the formation of indoxyl, the liquid is drained off and stirred continuously for several hours to stimulate oxidation of the indoxyl. Afterwards the solution is left to rest and the insoluble indigo settles to the bottom as a blueish sludge. The water is drained and after the indigo has dried, it is cut into cubes or made into balls. To dye textiles, indigo is reduced to a soluble form by a fermentation process under alkaline conditions. In traditional preparations of the dye, various reducing agents such as molasses are used, together with coconut-milk, bananas and the leaves of Psidium guajava L. The alkalinity is maintained by adding lime. After the textile has been dipped into the solution it turns blue when exposed to the air.
Indigo has been called "the king of dyes". No dye plant was as closely combined with culture as the indigo plant. The deep blue colour of the dye was highly appreciated, and its history is remarkable and covers thousands of years. However, the use of indigo of vegetable origin has nearly died out and it has been almost completely replaced by synthetic indigo. In recent years, interest in natural dyes has been increasing in many countries, not only because of concern about the environmental pollution caused by dye-producing chemical industries and the suspected injurious effects of synthetic dyes to health, but also because there has been a revival of interest in the relation between dyes and culture. Hopefully this new interest will gain ground rapidly enough to prevent indigo from disappearing completely as a crop in South-East Asia.
- Backer, C.A. & Bakhuizen van den Brink, R.C., 1963. Flora of Java. Vol. 1. Noordhoff, Groningen, the Netherlands. pp. 589-592.
- Byrne, M., 1981. Indigo dyeing: past and present. Journal of Consumer Studies and Home Economics 5: 219-227.
- de Kort, I. & Thijsse, G., 1984. A revision of Indigofera in Southeast Asia. Blumea 30: 89-151.
- Duke, J.A., 1981. Handbook of legumes of world economic importance. Plenum Press, New York. pp. 94-101.
- Krochmal, A. & Krochmal, C., 1974. The complete illustrated book of dyes from natural sources. Doubleday, New York. pp. 8-13.
- Oei, L. (Editor), 1985. Indigo, leven in een kleur [Indigo, life in a colour]. Stichting Indigo, Amsterdam, the Netherlands. 223 pp.
R.H.M.J. Lemmens & P.C. Wessel-Riemens