Indigofera tinctoria
(true indigo)

Preferred Common Name

• true indigo

Other Scientific Names

• Indigofera bergii Vatke
• Indigofera cinerascens DC.
• Indigofera houer Forssk.
• Indigofera indica Lam.
• Indigofera oligophylla Baker
• Indigofera orthocarpa (DC.) O.Berg & C.F.Schmidt
• Indigofera sumatrana Gaertn.
• Indigofera tinctoria Blanco
• Indigofera tulearensis Drake

International Common Names

• English: common indigo; Indian indigo
• Spanish: indigo
• French: indigotier
• Chinese: mu lan

Local Common Names

• Brazil: anil
• Cuba: añil; añil cimarrón; añil de Guatemala
• Germany: Faerber- Indigostrauch
• Haiti: digo digot
• Lesser Antilles: French indigo
• Myanmar: me; me-nai; me-net
• Puerto Rico: añil verdadero

EPPO code

• INDTI (Indigofera tinctoria)

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Fabales
•                         Family: Fabaceae
•                             Subfamily: Faboideae
•                                 Genus: Indigofera
•                                     Species: Indigofera tinctoria

Indigofera L.is the largest genus of the tribe Indigofereae, in the Fabaceae (Leguminosae) family, containing over 700 species found in the tropics and subtropics (Puy et al., 2002). Linnaeus (1753) described the genus based on the three species of I. tinctoria, I. hirsuta and I. glabra, with the name Indigofera referring to the indigo dye produced by members of the genus. Commonly called ‘true indigo’, the species name I. tinctoria reflects its status as a primary source of dye among the indigo plants.

Erect shrub to 1.5 m tall, many-branched from base. Leaves imparipinnate; leaflets opposite, 11-13, 1.5-2.5 × 0.7-1 cm, oblong, elliptic or oblanceolate, membranous, puberulent on lower surface, the apex mucronulate, rounded or seldom obtuse, the base tapering to obtuse, the margins entire; petiolules 1-1.5 mm long; stipules awl-shaped, 2-3 mm long, persistent. Racemes axillary, many-flowered, 5-10 cm long, sericeous; bracts minute, persistent. Calyx bell-shaped, 1-1.5 mm long, pubescent; corolla pink, tomentose without, the standard to 5 mm long, broadly elliptic, the wings and keel as long as the standard. Legume 3-3.5 cm long, curved only at apex, cylindrical, becoming glabrous, tardily dehiscent; seeds ca. 2 mm long, square-shaped to oblong (Acevedo-Rodríguez, 1996).

I. tinctoria was widely used as a textile dye and a medicine for centuries in Southeast Asia and India, although its origin remains obscure; indigo dye from several Indigofera species, mostly I. tinctoria, was found on the remains of an Egyptian mummy dating back to 2300 BC and the species has also been found in Inca tombs (MacLeod, 1997; Armitage, 2008). Pliny wrote of an Indicum plant that possessed similar properties to the modern Indigo, and in the 15^th century, the Venetians were in the habit of receiving Indigo from the East via Alexandria, Egypt (Macfadyen, 1837). After the discovery of the passage to India by the Cape of Good Hope, the Dutch were supposedly the first to import indigo directly into Europe in the middle of the 16^th century, although “it was long, however, where it came into general use as a dye, and there appears to have existed against it a very unaccountable prejudice. It…. was prohibited in England during the reign of Queen Elizabeth, and also in Saxony by the Elector, who described it in his edict as a corrosive substance, and fit food only for the devil” (Macfadyen, 1837).

I. tinctoria was reported (as syn. I. sumatrana) to have been introduced to Bengal, India in the mid-1700s for dye production, “either from Malabar or directly from Malaya, and proving a more satisfactory plant than either the Egyptian or the Indian kinds, has spread westward through Upper India as far as the Punjab and more recently southward to Madras. From Bengal it was taken to the West Indies” (University of Calcutta, 1902). Macfadyen (1837) writes that sometime after Queen Elizabeth’s reign indigo’s importance “came to be understood, and the cultivation of the plants which yield it was introduced into the West Indies, and into Mexico, and followed up with such success, that the market of Europe was for a long time principally supplied from these countries” instead of from the East, with a large portion being furnished by Jamaica.

The exact date of introduction of I. tinctoria to the West Indies is uncertain, but it was in Jamaica by 1837 (Macfadyen, 1837) and as of 1876 the species was recorded as ‘cultivated in former times but now only found wild or naturalized’ in St. Croix and other Virgin Islands (Eggers, 1876, 1879). It was included in an 1893 flora of St. Vincent (Kew Bulletin, 1893). The species occurred in Saint Kitts by 1901, Cuba by 1909, Curacao by 1914, and by 1924 it was known to occur in Vieques, St. Thomas, Florida, Hispaniola and from St. Martin to Grenada (Boldingh, 1914; Britton and Wilson, 1924). The first record of the species on the West Indies island of Navassa was a 1929 visual report by Erik Eckman (Zanoni and Buck, 1999). Specimens were collected from Martinique in 1885, Montserrat in 1907, Puerto Rico in 1914, Haiti in 1920, and St. Kitts-Nevis and St. Martin in 1932 (US National Herbarium). I. tinctoria was also known to be cultivated in Guatemala by 1854 as an alternative indigo source to the East Indies (Pereira, 1854).

I. tinctoria is very similar to I. suffruticosa and I. arrecta (see ‘Similarities to Other Species’ section), and in past records these three species have sometimes been confused. For example, Britton’s 1918 flora of Bermuda identifies the I. tinctoria of Jones, LeFroy and HB Small as I. suffruticosa, the only indigo species to be listed in Britton’s flora (Britton, 1918).

Soil drainage

• free
• seasonally waterlogged

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• light
• medium

I. tinctoria spreads by seeds (Duke, 1981). Dispersal by humans is primarily through intentional introduction as it has been cultivated for indigo dye production, for environmental purposes and for traditional/folk medicine. There is also accidental introduction as a cultivation escape, as well as by animals, as the leaves are rich in potash and the plant reportedly eaten by cattle in some places (Duke, 1981). I. tinctoria can also spread via water, as it can grow on sandy coastlines and riverbanks.

I. tinctoria has a positive impact on soil quality, serving as both a green manure and a cover crop, and has been widely used as such around the world. Using it as a green manure for rice increases yield while reducing the need to supply extensive nitrogen fertilizer to about half. The reside remaining after indigo extraction is also applied as manure. I. tinctoria is also a good N catch crop, reducing the amount of fertilizer NO3 leaching to the groundwater. However, the species possesses traits that pose a threat to native flora, as it is fast-growing, disperses easily by seeds and is easily transported by humans and animals.

I. tinctoria has been used as a hair dye and there have been concerns of its possible harm to human health. In April 2004, the Scientific Committee on Cosmetic Products and Non-Food Products identified the need for a complete safety dossier of the species, and a review of its potential toxicity was conducted by the EU Scientific Committee on Consumer Safety which concluded in 2012 that further research is required, as currently there is insufficient data (SCCS, 2012).

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Benefits from human association (i.e. it is a human commensal)
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year

• Ecosystem change/ habitat alteration
• Modification of nutrient regime
• Monoculture formation
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition - shading
• Competition - smothering
• Rapid growth

• Highly likely to be transported internationally deliberately

I. tinctoria was once the world’s primary source of Indian indigo, but was eventually replaced by I. arrecta, before the rise of synthetic indigo production replaced plant-based indigo dye (Duke, 1981). It has also been used as a cover crop in coffee plantations and rice fields, as green manure for crops such as maize, cotton, and sugarcane, as well as an occasional fodder crop, contrasting with the poisonous nature of some other members of the Indigofera genus (Duke, 1981; Lemmens and Wulijarni-Soetjipto, 1991). Although now made of synthetic dyes, painters in the past used I. tinctoria for the blue in their watercolours (Macfadyen, 1837). In Madagascar, the species was previously cultivated and is still used as a dye plant, while the pounded leaves are used as a compress or as a herbal tea (Puy et al., 2002). Other folk medicinal uses include the juice of the leaves as a prophylactic against hydrophobia, and as a decoction for blennorrhagia; plant extract as treatment for epilepsy, nervous disorders, bronchitis, and as an ointment for sores, old ulcers, and haemorrhoids; and roots for hepatitis, scorpion bites, and urinary complaints (Duke, 1981; Lemmens and Wulijarni-Soetjipto, 1991).