Woad (Isatis praecox)

A glaucous annual crucifer, with the lower leaves stalked and oblong and the upper ones sessile and arrow-shaped; small yellow flowers gathered in a corymb; pendulous silicles, indistinctly winged. From the leaves of this plant a blue colouring principle is extracted, capable of replacing indigo, which was once much used by Madeiran dyers. Madeira formerly exported some woad to Portugal, as can be seen from some notes that João Gonçalves Zarco received from Prince Henry the Navigator, in which he said: ‘let it be a reminder to you to send the woad once it has been prepared, and tell João Affonso to send some if it is prepared.’ Preparing the woad probably meant simply drying it in the sun, or else crushing its leaves, letting the resulting mass lose its water and forming it into balls, after allowing it to undergo the beginnings of fermentation for 8 to 12 days. Woad is not only useful in dyeing; it is also a fodder valued by cattle and sheep. In Câmara de Lobos (‘seals’ den’) its juice is used to treat pimples and other skin complaints.