Description---Blue Flag Rhizome has annual joints, 2 or more inches long, about 3/4 inch in diameter, cylindrical in the lower half, becoming compressed towards the crown, where the cup-shaped stem-scar is seen, when dry, and numerous rings, formed of leaf scars are apparent above and scars of rootlets below. It is dark brown externally and longitudinally wrinkled. The fracture is short, purplish, the vascular bundles scattered through the central column. The rootlets are long, slender and simple. The rhizome has a very slight but peculiar odor, and a pungent, acrid and nauseous taste.
Medicinal uses --- Its chief use is for syphilis and some forms of low-grade scrofula and skin affection. It is also valuable in dropsy. It is said to have been used by the southern North American Indians as a cathartic and emetic. The flowers afford a fine blue infusion, which serves as a test for acids and alkalies.
