INDIGO

Family: Fabaceae (Leguminosae), Indigofera species

Source: Simon, J.E., A.F. Chadwick and L.E. Craker. 1984. Herbs: An Indexed Bibliography. 1971-1980. The Scientific Literature on Selected Herbs, and Aromatic and Medicinal Plants of the Temperate Zone. Archon Books, 770 pp., Hamden, CT.

Indigo refers to several species of Indigofera, famous for the natural blue colors obtained from leaflets and branches of this herb. Of primary importance are French indigo, Indigofera tinctoria L., and Guatemalan indigo, Indigofera suffruticosa Mill., which was formerly classified as Indigofera anil L. These plants are perennial shrubs with an erect stem reaching a height of 1 to 2 meters. The French and Guatemalan indigo differ in size and shape of the leaflets and pods (14.1-3). Prior to the development of synthetic aniline and indigo dyes, the indigo species were grown commercially in the East Indies, India, and parts of North, South, and Central America for export and domestic use. Popularity and economic value of the plant reached a peak during the Middle Ages, when indigo was the most important dye plant for blue color in the western portion of the world (9.1-5).

The reported life zone of Indigofera tinctoria is 16 to 27 degrees centigrade with an annual precipitation of 0.7 to 4.2 meters and a soil pH of 5.0 to 7.3 (4.1-31). Indigo is generally grown as a perennial shrub, although in Morocco it grows as a biennial herbaceous plant (13.1-76).

The blue dyestuff is produced during fermentation of the leaves, commonly with caustic soda or sodium hydrosulfite. A paste that exudes from fermenting plant material is processed into cakes and finely ground. The blue color develops as the material is exposed to air (13.1-76). The indigo dye is a derivative of indican, a natural constituent of several of the Indigofera species (14.1-19). Indican is enzymatically converted to blue indigotin (14.1-35). The colorfast dye is mixed with different mordants and other plant materials to produce a wide range of colorants. The species name tinctoria refers to tinctorius, meaning "of dyes" or "belonging to dyes" (14.1-3). Today almost all indigo for dyeing cotton and wool is synthesized commercially.

As a medicinal plant, indigo has been used as an emetic. The Chinese use Indigofera tinctoria L. to clean the liver, detoxify the blood, reduce inflammation, alleviate pain, and reduce fever (11.1-10). The powdered root of Indigofera cf. patens is used in South Africa to alleviate toothache (11.1-96). Indigofera spirata is known as a plant teratogen because of the presence of indospicine (11.1-96). Indigofera endecaphylla plant, creeping indigo, is poisonous and has been responsible for livestock death (11.1-96). Indigofera arrecta Hochst. ex A. Rich and Indigofera caroliniana Mill. are used as dye plants (9.1-5).

False, wild, and bastard indigo are names for Baptisia tinctoria L., a native North-American member of the Leguminosae family, whose leaves, pods, and bark are used to make a blue color. Medicinally, it is employed as an astringent, emetic, stimulant, and antiseptic. Fake indigo and Baptisia leucantha are reported to have caused poisonings, diarrhea, vomiting, and loss of appetite (11.1-96, 11.1-136). Strobilanthes flaccidifolis and Dalea emoryi L., known as indigo bush, have been used as indigo dye plants.

[Note: References listed above in parentheses can be found in full in the original reference].


Aromatic and Medicinal Plants Index

Last modified 6-Dec-1997