Common Name:

General Information

Indigofera longiracemosa is an erect, branching rather woody annual or short-lived perennial herb; it can grow up to 2 metres tall with slender, cylindrical, red-brown, sparingly strigulose stems[, ].
Indigo, of which this species is a minor 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 and it is now only grown on a small scale in places such as Madagascar and Indonesia[]. In some areas, especially Madagascar, this species is held to provide a superior dye to other Indigo species and it was widely used on both a domestic and an industrial scale until late into the 20th century[].

Known Hazards

None known

Botanical References

Range

East tropical Africa - Kenya, Tanzania, Madagascar.

Habitat

Lowland, usually coastal regions, in dune vegetation or grassland on sand, often around villages, at elevations up to 200 metres[].

Properties

Medicinal Rating
Other Uses Rating
Habit	Annual/Perennial
Height	1.30 m
Pollinators	Insects
Cultivation Status	Cultivated, Wild

Cultivation Details

A plant of lowland areas in the tropics, where it can be found wild at elevations up to 200 metres[]. In Indonesia it is cultivated at alevations around 1,650 metres because it is attacked by pests at lower elevations[]. The plant grows wild in areas where the mean annual rainfall is in the range 1,000 - 1,500mm[].
Indigo species generally grow best in a sunny position, preferring a well-drained but moist soil[]. Many of the species will also succeed in drier conditions and in poor soils.
We have seen no specific information for this species, but most members of the genus have 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

None known

Medicinal

A decoction of the leaves is used as a diuretic[].

The root has been used as an antidote for snake poisons[].

Agroforestry Uses:

The plant is used as a green manure[].

Other Uses

The leaves are used to produce the 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[].
Indigofera plants contain the glucoside indican. After soaking the plants in water or pounding the leaves, enzymic hydrolysis transforms indican into indoxyl and glucose. Indoxyl is then oxidized and polymerized to indigotin (indigo-blue). Indigotin is insoluble in water, so to dye textiles it must be reduced to a soluble 'leuco' or colourless form (indigo-white) by a chemical or fermentation process under alkaline conditions. The cloth to be dyed is soaked in this solution. Subsequent re-oxidation of the indigo-white results in the precipitation of the blue indigo colour on the textile. Natural indigo also contains varying proportions of the chemically related dye compounds: indirubin (red), isoindirubin (red) and isoindigo (brown)[].
The harvested plants are stacked in a big container (a barrel with a tapped hole at the bottom). Water is added to cover the plants and they are weighed down with a stone. The plants are left under water for about 12 hours, or as long as air bubbles come to the surface. Then the extraction water is drained off through the hole at the bottom into another container. It is mixed with a solution of slaked lime (in volume proportion 3:1) and well beaten to bring in oxygen and allow the formation of indigotin. Agitation and the addition of small amounts of lime water continue until blue indigo particles are formed. Now stirring continues but without addition of lime water. Then the liquid is left undisturbed for some time to allow the indigo to precipitate on the bottom. After pouring off the waste liquid, the indigo paste is collected into a mould with small holes on all sides that allow the evacuation of remaining water. When the paste is firm enough, it is taken out of the mould and the loaf is left to dry in the shade (sun would taint it pale blue). When dry the loaves are cut and packed, being ready for use or trade. Out of 10 kg fresh leaves, this domestic scale method produces 26 g of indigo with an average indigotin content of about 31%[].
The magnificent raffia textiles called 'lay masaka', are still produced by traditional means in Madagascar, mainly for the tourist market. These textiles have ornate designs made with an 'ikat' technique in which parts of the warp yarns that are to remain undyed are tightly entwined with a thick thread. The yarns are then dyed and set on the loom, whereby the undyed parts of the yarn form a light-coloured pattern on a dark ground. Other natural fibres such as silk, cotton and wool, absorb indigo blues more easily using a dye bath and the colour is more pronounced[].

Propagation

Seed - it has a hard seedcoat and may benefit from scarification before sowing in order to speed up and improve germination. 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.

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