Chlorociboria aeruginascens (Nyl.) Karst. ex Ram syn.. Chlorosplenium aeruginascens (Nyl.) Karst. Grüner Holzbecherling Chlorosplenium blue-vert, Green Elfcup. Fruit body 1–5mm across, cup-shaped then flattened with a wavy, irregular margin, attached to the substrate by a short stalk, bright blue-green throughout. Asci 70 x 5m. Spores fusiform, containing two small oil drops situated at opposite ends of the spore, 6–10 x 1.5–2µ. Habitat on fallen branches of deciduous trees, especially oak. The mycelium growing through the wood stains it conspicuously blue-green. Season mainly autumn although also found in spring to autumn. The stained wood is often seen but the fruit bodies are less frequent. Not edible. Distribution, America and Europe.
The infected wood, known as ‘green oak’, was formerly used in the manufacture of Tunbridge ware, a traditional method of decoration where woods of different colours were arranged into blocks to give the desired pattern, compressed, then cut transversely into thin strips of veneer.