aka Hop hornbeam disc (even though I usually see it on mature oaks.) You usually see the odd patches of smooth bark on mature oak trees first (see last photo), and then upon close examination find the tiny little irregularly shaped discs, tan in the center, with the hairy white undersurface curling over and showing on the front, encircling the tan center forming a shallow bowl shape. https://www.messiah.edu/Oakes/fungi_on_wood/crust%20and%20parchment/species%20pages/Aleurodiscus%20wakefieldiae.htm calls A. oakesii the synonym for A. wakefieldiae, but here A. wakefieldiae is called pink disco, and the Slovenian observation here looks like a pink blob on a branch, not A. oakesii-like. I see from https://sites.google.com/site/scottishfungi/species-profiles/aleurodiscus-wakefieldiae that A. wakefieldiae is truly pink, and seems to prefer branches, not mature oak bark, so I am following Michael Kuo at http://www.mushroomexpert.com/aleurodiscus_oakesii.html and Tom Volk at http://botit.botany.wisc.edu/toms_fungi/apr2006.html and calling this A. oakesii.