Eupatorium perfoliatum, also known as Common Boneset or Thoroughwort, is a well-known perennial plant native to the Eastern United States and Canada. It is often found in low, wet areas and is used in traditional medicine in North America for treating influenza, colds, acute bronchitis, catarrh, and skin diseases. It is also known to stimulate resistance to viral and bacterial infections and reduces fevers by encouraging sweating. However, large doses of this plant may cause laxative and emetic effects and may contain potentially liver-harming pyrrolizidine alkaloids. Eupatorium perfoliatum is distinctive with its perfoliate leaf bases and is extraordinarily widespread, and hybrids between Eupatorium species have also been reported. It is a specific food and habitat plant for the White M hairstreak and the Bronze Copper butterfly.