Book IV of Dioscorides’ pharmacological treatise De materia medica includes an apocryphal interpolation on the μυροβάλανον κίτρινον. This short text is present both in the Aldine edition of 1499 and in twelve manuscripts, the oldest of which is Par. gr. 2183, copied at the Monastery of St John Prodromos at Petra in the middle of the 14th century. I here offer the Greek text along with a Spanish translation and commentary. I pay special attention to a number of botanical terms foreign to classical Greek, to which Greek-Eastern botanical glossaries transmitted in many Byzantine manuscripts assign an Arabic origin. I argue that the main source for this interpolation is a text by the Byzantine doctor Ioannes Zacharias Aktouarios, a good connoisseur of Arabic medicine. The library-scriptorium of the Monastery of St John Prodromos was presumably the place where this interpolation was carried out.