Since classical times and possibly much earlier, hundreds of species of plants have provided drugs to treat a wide range of conditions. Dioscorides's De Materia Medica, written by 70 AD, listed some 600 medicinal plants and around 1000 drugs made from them, including substances known to be effective such as aconite, aloes, colocynth, colchicum, henbane, opium and squill. The book remained a standard reference for nearly two thousand years, and was the basis of the European pharmacopoeia until the end of the 19th century.[32][33]