Thelotrema ...

[BubikolRamios]

On Acer, south Slovenia, karst region: http://agrozoo.net/jsp/Galery_one_image ... a318986cac ?
Not very clear image as things are small, focus on part direct above "0.5 mm", sausage like crater rim.

Looks like thallus can be aerolate: http://www.nature-bretagne.net/pages/li ... adinum.htm

[bryotom]

Hello,
the first link shows not convincing photos. This could well be something different.
The ones from the Bretagne show clearly and unambiguously Thelotrema lepadinum.
You may look out for better specimens.