Arthonia punctiformis Ach.
Thallus very thin, immersed in bark, usually effuse, indistinct or slightly 'bleaching' the bark: whitish, pale grey, pale brown, prothallus absent. Apothecia scattered all over the thallus, usually immersed, flat and non erumpent, variable in size and shape, rounded, elliptic to linear, rarely branched or substellate, 0,2-1,2 mm, black, not pruinose. Ascospores colourless, oblong-ovoid to oblong, 3 (-5)-septate, apical cell not enlarged, 15-23 x 5-7 µm. Photobiont : Trentepohlia. Chemical spot test negative. Often a primary common colonizer on smooth bark of twigs of a wide variety of deciduous trees and shrubs. Often associated with Arthopyrenia punctiformis but with ascospores uni-septate. N.B. This species does not seem to have photobiont and probably is not lichenized.*