The mala medica is the tree you see in the back of Botticelli’s Primavera that has white flowers and orange fruits growing on it at the same time. You can see the very same type of tree in other works in this room, including the Madonna Enthroned with Saints by Domenico Ghirlandaio of 1484, in which the fruit is large and significant. There's some confusion as to what the Mala Medica is. The word “mala” is similar to mela, apple in Italian, but in these paintings it's depicted as an orange and is definitely part of the citrus family. Dr. Albert Shneider writes of the Mala Medica in his 1899 article on BirdNature:
Lemons have been known for a long time. They were brought to the notice of the Greeks during the invasion of Alexander the Great into Media where the golden-yellow fruit attracted the attention of the warriors who gave them the name of Median applies (Mala medica). Later, Greek warriors also found this fruit in Persia, and hence named it Persian apples (Mala persica). The eminent Greek philosopher and naturalist Theophrastus, 390 B.C., described the fruit as inedible, though endowed with a fragrant odor, and having the power to keep away insects. On account of this latter property the so-called Median apple was, by some, supposed to be identical with the fruit of the cedar (Kedros) and therefore received the name “Citrus” from which is derived “citrone,” the German name, and “citronnier,” the French name for the fruit.
In any case, the mala medica, also known as mala aurantia or melarancia in Italian supposedly has therapeutic properties for the digestive system. The Medici family of Florence adopted it as part of their iconography. Medici means doctor in Italian, and the mala medica is a perfect example of wordplay. When you see what looks like oranges in art of this period, you can safely assume that the piece was a Medici commission.