Polygonum tinctorum

Redshank
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Core eudicots
Order:	Caryophyllales
Family:	Polygonaceae
Genus:	Persicaria
Species:	P. tinctoria
Binomial name
Persicaria tinctoria (Aiton) H.Gross

''Persicaria tinctoria (Aiton) H.Gross'' (syn. Persicaria tinctoria (Aiton) Spach, formerly known as Polygonum tinctorum L.^{[citation needed]}, Polygonum tinctorium Aiton, Polygonum tinctorium Lour., Ampelygonum tinctorium (Aiton) Steud., Pogalis tinctoria (Aiton) Raf.) is Chinese indigo, a plant of the Buckwheat family that is found from Eastern Europe to East Asia, and whose leaves were the source of blue dye called Indigo dye. This plant will grow in sandy, loamy and heavy clay soils, and is pH tolerant, growing well in acid and alkaline soils.

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.

This plant was commonly called "Dyer's Knotweed."

External links

• About indigo
• Polygonum tinctorium/ Japanese indigo