Persicaria tinctoria

Persicaria tinctoria is a species of flowering plant in the buckwheat family. Common names include Chinese indigo and "Japanese indigo." It is native to Eastern Europe and Asia.

The leaves were a source of indigo dye. It was already in use in the Western Zhou period (ca. 1045-771 B.C.), and was the most important blue dye in East Asia until the arrival of Indigofera from the south.