Isatis tinctoria is a flowering plant in the family Brassicaceae, from whose leaves a blue dye is produced (the flowers are yellow). It is commonly known as woad or Asp of Jerusalem. The common names in Italian, German, and French are guado or gualdo, Färberwaid, respectively pastel des teinturiers or guède. It was used with weld (for yellow) and madder (for red) to produce full color images from at least the Neolithic Age, when it was introduced in Europe.
With the European discovery of the seaway to India, woad was replaced with indigo or Indigofera tinctoria, which contains the dye in higher concentration. Today, synthetic indigoes are used. However, Isatis tinctoria still has use in some inkjet inks because it is biodegradable.