Isatis

Isatis is a genus of flowering plants in the mustard family, Brassicaceae. It comprises several species native to Europe, western Asia, and North Africa. The most notable species are Isatis tinctoria, commonly known as woad, and Isatis indigotica, often called indigo woad. Both have been valued historically for their production of blue dyes.

Isatis plants are hardy and typically herbaceous, with a growth habit that can be biennial or short-lived perennial. They usually form a rosette of bluish-green leaves in the first year, followed by flowering stems bearing small white to pale yellow flowers. The seed pods are slender and elongated, typical of many mustard relatives.

Historically, woad has been cultivated for its leaves, which contain indican. Through processing and oxidation, indican is converted to indigotin, the blue dye used for textile coloring. Woad dyes were widely used in Europe before the rise of synthetic indigo. Indigo woad from Isatis indigotica has also been used in East Asia for similar dyeing purposes.

Cultivation and ecology vary by species, but Isatis generally tolerates a range of soils and climates in temperate regions. They are sometimes grown as ornamental or landscape species in addition to their historical dye-related roles.

Etymology and taxonomy place Isatis firmly within Brassicaceae, a large family that includes many familiar cruciferous plants. The genus name Isatis is a traditional botanical designation dating back to classical sources.