Where does indigo dye come from?

Asian plants, mostly Indigofera tinctoria (aka Indigofera sumatrana) were the original source for the dye, with several thousand square kilometers of the plants grown in India around 1900.

A variant found in the Americas is Indigofera suffruticosa, known as aƱil in the West Indies. The name for now-synthetic aniline dyes comes from this name.