Blessed thistle, or cnicus benedictus, is in the family Asteraceae. It is an annual plant with hairy leaves and yellow flowers. During the Middle Ages, it was commonly used to treat the bubonic plague. It is a bitter herb that contains tannins and has been used to increase the flow of gastric and bile secretions. Prepared as a tea, it may help indigestion. It has also been used externally as an antiseptic.