Taphrina pruni Taphrina pruni Taphrina pruni is a fungal plant pathogen of blackthorn (Prunus spinosa) that causes the Pocket or bladder Plum gall, a chemically induced distortion of the fruit (sloes), producing swollen on one side, otherwise deformed and flattened fruit gall without a stone. The twigs on infected plants may also be deformed with small strap-shaped leaves. "T. pruni" produces a distinctive tongue-like growth, similar to other closely related species such as "Taphrina alni" on Alder ("Alnus glutinosa") and "Taphrina padi" on Bird Cherry "Prunus padus". The growth is the distorted fruit and not a fungus in its entirety. "T. pruni"
Prunus avium parent species of "Prunus cerasus" (sour cherry), by way of ancient crosses between it and "Prunus fruticosa" (dwarf cherry) in the areas where the two species overlap. All three species can breed with one another. "Prunus cerasus" is now a species in its own right, having developed beyond a hybrid and stabilised. Pliny distinguishes between "Prunus", the plum fruit, and "Cerasus", the cherry fruit. Already in Pliny quite a number of cultivars are cited, some possibly species or varieties, Aproniana, Lutatia, Caeciliana, and so on. Pliny grades them by flavour, including dulcis ("sweet") and acer ("sharp"). and goes so far