Common Name: Bengal Indigo

General Information

Indigofera arrecta is a stout, copiously-branched, perennial herb usually growing 30 - 200cm tall, occasionally to 300cm[]. The spreading or ascending stems can become more or less woody and persistent[, ].
Indigo, of which this species is a major source, has a very long history of use as a 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, it has been called 'the king of dyes' and no other dye plants have had such a prominent place in as many civilizations as this genus. It was at one time widely cultivated for this purpose but, with the advent of synthetic dyes, demand for the plant dropped dramatically[]. It is still sometimes cultivated for its dye, especially in India, but on a much reduced scale[]. The plant has many applications in traditional medicine and is also occasionally eaten. In many tropical countries of Asia and Africa the species is grown however as cover crop for tea, coffee and Hevea plantations, as green manure for rice and cotton and as a contour hedge plant for various plantation crops[]. It is also used often in the indigenous folk medicine[].

Known Hazards

None known

Botanical References

Range

Tropical Africa - widely distributed throughout the continent from Senegal to Somalia, south to S. Africa. Also extending into Arabia.

Habitat

Deciduous and evergreen bushland; mixed woodland areas of cultivation and secondary growth; forest margins; (Hyparrhenia) grassland; roadsides; flood plains; pans; termitaria; waste ground; at elevations of 200 - 2,700 metres[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Perennial
Height	2.00 m
Cultivation Status	Cultivated, Wild

Cultivation Details

A plant of the moist tropics, where it is found at elevations from 300 - 2,700 metres. It grows best in areas where annual daytime temperatures are within the range 22 - 30°c, but can tolerate 16 - 36°c[]. It can be killed by temperatures of °c or lower[]. It prefers a mean annual rainfall in the range 1,700 - 2,200mm, but tolerates 400 - 4,300mm[].
Prefers a hot, moist climate and a position in full sun[]. Succeeds in a range of soils[]. Prefers a pH in the range 5 - 6, tolerating 4.5 - 6.5[]. Plants can tolerate up to two months of waterlogging[].
Plants can commence flowering 3 months after sowing the seed[].
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 also 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, whilst for cover crops it is 1.5 - 2 years[, ].
Indigo is harvested only once when grown on paddy soils because the plants must give way for the next rice crop[].
The yield of this species is higher than from any other species of Indigofera. Annuals yields of 22 - 100 tonnes green matter per ha have been reported in India; the recorded output of indigo cake is 137 - 325 kg/ha per year[].
Natural hybridizations between Indigofera arrecta and Indigofera tinctoria do occur and especially in W Africa plants are often difficult to be assigned to one of the two taxa[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

Young leaves - cooked and eaten as a vegetable[].

Medicinal

The leaves are used in traditional medicines for treating diarrhoes, dysentery, epilepsy and nervous disorders[, ]. An aqueous extract of the leaves from immature shoots is administered orally to patients with diabetes mellitus[]. A medicine for the management of peptic ulcer and methods of its preparation and use have been patented[].
The leaves are applied externally to heal sores and ulcers[].

An infusion or decoction of the leaves and roots is abortifacient, antispasmodic, diuretic, febrifuge, purgative, sedative, stomachic and vermifuge. It is used to treat conditions such as gum infections, snakebites, gonorrhoea, epilepsy and jaundice[].
The leaves and roots are used externally to treat itching[].

The fruits and seeds are used to treat ophthalmia[].

In several regions in Africa it is believed that the indigo dye in clothes prevents skin complaints[]

Agroforestry Uses:

The plant has potential as a cover-crop and green manure, especially in tea, coffee and rubber plantations[, , ]. It gives shade and protection, suppresses weeds and improves the soil[].
The residue remaining after indigo extraction is also applied as manure[].

Other Uses

The plant is a major source of the blue dye 'indigo'[]. The leaves and twigs do not actually contain indigo but colourless precursors that must be extracted and then processed in order to produce the indigo dye[].
The harvested leafy branches are placed in a tank containing water to which some lime has been added, and are 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 then 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 bluish 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[]. The alkalinity is maintained by adding lime. After the textile has been dipped into solution it turns blue when exposed to the air[].

The twigs are used for cleaning teeth[].

Propagation

Seed - it possess a hard seed-coat and must be scarified[]. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing. 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[].

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