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Isatis is a genus of flowering plants in the mustard family, Brassicaceae. The most famous member of this genus is I. tinctoria, known by the common name of woad or dyer's woad. In addition to producing a famous dye, this plant has also historically been used in both Ayurveda and traditional Chinese medicine, where it is believed to be beneficial for people with respiratory complaints and fevers. Some gardeners cultivate woad because they are interested in producing natural dyes.
Members of this genus produce basal rosettes of leaves and long stalks with bright yellow flowers. They are native to the Mediterranean and have spread through much of Europe and parts of Asia, along with other members of the mustard family. Isatis is adapted to grow in a variety of soils, including very harsh soils, and it can thrive in salty and cold conditions. This durability can become a disadvantage in settings where Isatis is invasive.
Woad has been cultivated since the Neolithic era, as numerous archaeological sites have demonstrated. The blue dye produced from this plant has been used in the production of textiles, body paints, inks, and a variety of other products. Sources of blue dye are relatively rare in nature and as a result, strong blue dyes were highly prized by many societies. Isatis was one potential source for the blue known as indigo in regions where true indigo plants could not grow due to climate conditions.
In traditional Chinese medicine and Ayurveda, the roots of Isatis are used in the treatment of some medical conditions. The efficacy of these plant products in medical treatment has not been widely tested. It is possible that the plants may contain some compounds with uses in medical treatment, and there are no known contraindications for treatment with products made from Isatis, although because the plant has not been tested in pregnant women, expecting mothers may want to check with their doctors before taking it.
Commercially, Isatis species are cultivated in several regions of the world. They are not widely used as a source of dye because synthetic indigos are more colorfast and much easier to obtain, with most cultivation for dye purposes being done by individuals interested in using traditional plant dyes. In Asia, Isatis tinctoria is grown for the purpose of producing medicinal preparations. In some regions like the United States, volunteer plants have become aggressively invasive and are a conservation problem.