Acanthotrema kalbii

Acanthotrema kalbii is a species of corticolous (bark-dwelling) lichen in the family Graphidaceae. First classified as a new species in 2012, the lichen is found in Costa Rica, where it grows in partially shaded areas of disturbed primary forest within the montane rainforest zone. This lichen stands out from its close relative, A. brasilianum, primarily due to the internal structure of its larger ascospores. The inaugural specimen of A. kalbii used for the species' formal description, was located on tree bark in a montane rainforest in the Las Tablas Protected Zone. The lichen is recognisable by its grey-green thallus, which varies from smooth to uneven and produces slender isidia, tiny outgrowths, up to 2 mm in length....read more on Wikipedia.