The outer tissue layer of the apothecium is bright green and smooth on the top, and felty and pale blue-green on the underside and stipe, darkening with age.

Apothecia grow on bark-free wood, especially oak, beech and hazel, part of which at least is stained greenish by the mycelium.

Both C. aeruginosa and C. aeruginascens contain a quinone pigment called xylindein,[6][7] a dimeric naphthoquinone derivative, whose structure was determined by spectroscopic means in the 1960s [8] and later confirmed by X-ray crystallography.

[9] It is this compound that is responsible for the characteristic bluish-green stain of wood infected by thosespecies, used today in decorative woodworking such as Tunbridge ware[10] and parquetry.

[11] The use of this wood, known as "green oak", goes back to 15th century Italy, where it was used in intarsia panels made by Fra Giovanni da Veroni.