Inoderma byssaceum

Inoderma byssaceum is a species of corticolous (bark-dwelling) crustose lichen in the family Arthoniaceae. It forms a thin, whitish crust on tree bark and is recognised by its conspicuous white-frosted fruiting bodies that resemble tiny cups dusted with powder. The lichen grows primarily on old oaks in humid forests across the temperate Northern Hemisphere and has declined markedly in recent decades, leading to its inclusion on numerous national red lists. Originally described in 1772 from oak bark in Germany, the lichen serves as the type species for the genus Inoderma, a genus characterised by these distinctive white-pruinose reproductive structures....read more on Wikipedia.