|Photo: Ray Woods||Photo: Alan Orange|
A member the Graphidion, a community of lichens confined to smooth bark, its pale olive-green or yellow-buff immersed thallus is often barely perceptable to the untrained eye on the somewhat similar coloured bark of old hazel trunks. Occasionally small white dots are present. Immersed in the thallus are clusters of black perithecia (each perithecium 1 to 1.2mm in diam) that if visible give the lichen its English name of blackberries and custard as the perithecia grow in blackberry-like clusters and the thallus can be yellowish like custard. Unfortunately, as with the Welsh population, the perithecia are often almost invisible from the surface. No other large crustose lichen has such clusters of perithecia with the ostiole through which the spores are dicharged offset to one side. Unlike all other Pyrenula species the spores in this species are muriform.