A shrubby legume and one of Africa's main sources of natural blue indigo dye, historically used to dye skin and cloth across West Africa.
Bengal or Natal indigo (Indigofera arrecta, family Fabaceae) is a stout, much-branched perennial herb usually 30 to 200 cm tall and occasionally 3 metres, with stems that can become woody. It is a major source of indigo, a dye with a very long history: because of its deep blue colour, its fastness to light and the range of colours it gives with other natural dyes, indigo has been called "the king of dyes". The plant was once widely cultivated for dye, but demand fell sharply with the arrival of synthetic dyes, and it is still grown for dye mainly in India. It has many uses in traditional medicine, is occasionally eaten, and in tropical Asia and Africa is grown as a cover crop in tea, coffee and rubber plantations, as green manure for rice and cotton and as a contour hedge.
It is widely distributed in Africa from Senegal to Somalia and south to South Africa, extending into Arabia, in bushland, woodland, forest margins, grassland, farmland and regrowth, roadsides, floodplains, termite mounds and waste ground, at 200 to 2,700 metres. It prefers a hot, moist climate, full sun and slightly acid soil, and it tolerates up to two months of waterlogging. It can flower three months after sowing; for dye the branches are cut, usually early in the morning, at four to five months and then every three to four months, up to three times a year, and dye crops last two to three years. It yields more than any other indigo species. The hard seed must be scarified and germinates in about four days, and cuttings 30 cm long root within two weeks.
Source: Useful Tropical Plants database (Fern, K.).
Leaves are soaked and fermented to release the dye; this species yields notably more indigo than related indigo plants.