…plants through history, but most came from the “Indigofera” plant genus, which are native to the tropics and specifically from India. Another species called “strobilanthes” from Japan’s Ryukyu Islands and Taiwan produces indigo.
Dyer’s knotweed (“polygonum tinctorum”) was the most important blue dye in East Asia until the “Indigofera” was discovered to yield more dye per plant.
(Ancient sketch showing process of extraction of indigo in India)