There is no single "indigo plant". A variety of plants have been used to produce indigo dye.

Most natural indigo dye is obtained from plants in the genus Indigofera, which are native to the tropics. In Europe, indigo can be obtained from woad (Isatis tinctoria) and dyer's knotweed (Polygonum tinctorum). The primary commercial indigo species in Asia is true indigo (Indigofera tinctoria), a shrub found in Southeastern Asia. Its flowers range from red to purple.

For more information on indigo's history and uses, see indigo dye.