Pedanius Dioscorides (c. 40 – 90 AD) was a Greek physician, pharmacologist, botanist, and author of De materia medica (On Medical Material), a 5-volume Greek encyclopedia about herbal medicine and related medicinal substances (a pharmacopeia), that was widely read for more than 1,500 years. It was the precursor to all modern pharmacopeias. He was employed as a physician in the Roman army. The plant genus Dioscorea, which includes the yam, was named after him by Linnaeus.