St. John's wort. 16th century Italian illustration of St. John's wort (Hypericum perforatum), by Gherardo Cibo, 1568. St. John's wort is used medicinally to treat depression. This plate is taken from Discorsi on Dioscorides' De Materia Medica by Pietro Andrea Mattioli, a work of herbal medicine first published in Italy in 1554. Pietro Andrea Mattioli (1501-1577) was an Italian doctor and naturalist who wrote commentaries on De Materia Medica , an encyclopaedia of herbal medicine by the first century Greek physician and botanist Dioscorides.