Digital source of illustration (retrieved 7th July 2016).
GVE
Indigo
Indigofera tinctoria.
Indigo (Indigofera species) is a tropical plant of the genus Indigofera, which is a commercially important source of the blue dye stuff, indigotine. The most important indigo plant form is Indigofera tinctoria (also known as Indigofera sumatrana).
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Dyes