Definition
Isatis tinctoria, commonly known as woad, is a flowering plant historically significant as a source of blue dye. Belonging to the mustard family (Brassicaceae), it was cultivated throughout Europe for centuries. The plant's leaves contain a compound that, when fermented, produces a blue pigment used in dyeing textiles. Though largely replaced by synthetic dyes, woad remains historically important. Consider it the OG blue dye!