Epimedium, also known as barrenwort, bishop's hat, fairy wings, horny goat weed, rowdy lamb herb, randy beef grass or yin yang huo. Many species of Epimedium have aphrodisiac qualities associated with content of icarin. According to legend, this property was discovered by a Chinese goatherder who noticed sexual activity in his flock after they ate the weed. Icariin is purported to work by increasing levels of nitric oxidde, which relax smooth muscle. It has been demonstrated to relax rabbit penile tissue by nitric oxide and PDE-5 activity. Other research has demonstrated that injections of Epimedium extract directly into the penis of the rat results in an increase in penile blood pressure.