Goldenseal ( Hydrastis canadensis) grows in eastern North America, where it's now threatened in the wild. An alkaloid in goldenseal, berberine, shows powerful antimicrobial effects against a wide range of bacteria, yeasts, and parasites. Herbalists prescribed goldenseal to stimulate the immune system, fight infection, and treat diarrhea. (Podcast: The Plant Detective , 9/13/14)