Dyer's woad, or simply woad, is a biannual plant. In the first year, it only develops a rosette of leaves close to the ground. In the second year, it grows a stem of about three feet with lots of small, dark yellow flowers in clusters. The arrow-shaped leaves that surround the stem are bluish-green and contain the indigo precursor substances isatan A and B, indoxyl-derivatives. Isatans differ from the indican in Indigofera tinctoria and other indigo plants only in that instead of glucose being bound to the indoxyl,they are bound to D-ribohexo-3-ulopyranosides. When this is split from the isatans, however, the yellow indoxyl and sugars result, just as with the splitting of indican.
