Indigofera is a genus of about 700 flowering shrubs, herbs, and small trees, originally native to Pakistan, but now naturalized throughout tropical and subtropical regions of the world. They belong to the pea family, Fabaceae. Some Indigofera species are used to produce the dark blue dye indigo.
Blue dyes were once rare, and Indigofera plants, particularly I. tinctoria and I. suffruticosa, were important as a cash crop in the early colonial period of the Caribbean and the American South. Some herbs in the genus also have uses in traditional medicine. Many Indigofera species are also grown as ornamental plants today.
I. tinctoria, or true indigo, is one of the first plants used to make indigo dye. It is also one of the few sources of commercially available natural dye. I. tinctoria is also planted as a ground cover, as it has the ability to improve soil. I. tinctoria features pink to purple flowers. The dye is harvested from the leaves.
I. suffruticosa, or añil, grows throughout tropical and subtropical regions of the Americas, as well as in the Pacific Islands. It often grows in dry, disturbed soil, such as in fallow fields or by the roadside. I. suffruticosa was used to make Maya Blue, a bright blue pigment used by pre-contact Mesoamerican cultures. The chemical aniline, which is used in dyes and in the processing of rubber and plastic, was first isolated from I. suffruticosa and gets its name from the common name of the plant.
I. australis is one of the southernmost growing species. It is widespread in southern Australia. The plant is a popular ornamental in Australia because it grows well in a variety of conditions. It also has beautiful pink to lavender flowers that bloom in the spring.
While many Indigofera species are used to make dark blue dye, the stems and leaves of I. australis are used to make a yellow dye. The leaves of the plant are also used by Aborigines to aid in catching fish and eels. The crushed leaves are thrown in the water, and the chemicals they release stun or kill fish.
I. articulata has historically been used to treat toothache. I. oblongifolia has been used for its properties as an anti-inflammatory painkiller, particularly in the treatment of snake and insect bites. Other species, including I. aspalthoides and I. suffruticosa, have also been valued for their anti-inflammatory properties. I. arrecta has recently been considered in the treatment of pain caused by ulcers.