Persicaria tinctoria is a species of flowering plant in the buckwheat family.

Common names include Chinese indigo, Japanese indigo and dyer's knotweed.

[2][3][4] It is native to Eastern Europe and Asia.

The leaves are a source of indigo dye.

It was already in use in the Western Zhou period (c. 1045 BC – 771 BC), and was the most important blue dye in East Asia until the arrival of Indigofera from the south.