Chondostereum purpureum (Fr.) Pouz. syn. Stereum purpureum (Fr.) Fr. Purpurner Schichtpilz Stereum pourpre, Silverleaf Fungus. Bracket 1.5–3cm across, 1–2cm wide, 0.2–0.5cm thick, usually several brackets fused together and overlapping; extremely undulate, tough when fresh becoming brittle when dry; upper surface covered in dense white woolly hairs in concentric bands; lower surface dark violaceous or violaceous-brown in young specimens and becoming brownish with age, drying paler (lower specimens in photograph). Spores subcylindrical, 5–8 x 2.5–3µ. Hyphal structure monomitic; generative hyphae with clamp-connections. Habitat parasitic or saprophytic on various trees, especially members of the Rosaceae. Season all year. Common. Not edible. Distribution, America and Europe.
This fungus is the cause of ‘silver leaf’ disease which leads to the destruction of fruit trees; plum trees are particularly susceptible. The first visible sign of infection is silvering of the leaves due to the upper epidermis becoming separated from the rest of the leaf and lifting in patches. This effect occurs progressively along a branch and on cutting the wood appears stained brown by the fungus. If the wood is cut back until no infection is seen and the wound treated with a fungicide the fungus can be eliminated.
Where silvering of the leaves occurs all over a tree simultaneously it is unlikely to be due to this fungus; this can be verified by examination of the wood for staining. This false silver leaf which has the same symptom, that of the upper epidermis lifting, is caused by physiological disturbance such as heavy pruning.