Blue Flag Herb

My son needs information on a herb called Blue Flag. Have you heard of it and could you send us in the right direction to find more information?

Blue flag is a wild iris, Iris versicolor. It is native to wetlands in eastern North America. The thick thick rootstock is used medicinally. According to John Lust's "The Herb Book" (available from Richters), the roots are used for "chronic vomiting, heartburn, chronic gastritis and enteritis, liver and gallbladder ailments, and catarrhal sinus problems." Lust says it is "highly recommended" for migraine caused by stomach disorders. The root is acrid and can cause dermatitis or gastrointestinal irritation is some people.