Woad
Woad is a flowering plant that was cultivated to produce indigo dye. It is native to the Mediterranean, Central Asia, and Europe. It was historically produced in England, France, and Germany in medieval times. Eventually, the Indigo plant replaced woad as Europe's main cash crop that produces indigo dye. Woad also has medicinal properties, as an astringent. Romans referred to Celts of northern Britain as Picts because they used woad to heal their battle scars, producing a blue tattoo.