Isatis tinctoria
Until the introduction of "Indigofera" species from the south, "Polygonum tinctorum" ("Dyer's knotweed") was the most important blue dyestuff in East Asia; however, the crop produced less dyestuff than the average crop of indigo, and was quickly surpassed in terms of favour for the more economical "Indigofera tinctoria" plant. In Central and South America, the species grown is "Indigofera suffruticosa", also known as "anil", and in India, an important species was "Indigofera arrecta", Natal indigo. In Europe, "Isatis tinctoria", commonly known as "woad", was used for dyeing fabrics blue, containing the same dyeing compounds as indigo, also referred to as indigo.