Rinodina exigua

Rinodina exigua is a species of lichen belonging to the family Physciaceae, characterised by its thin, pale grey-green thallus (body) with an irregular, cracked surface. First described by Erik Acharius in 1798, it features distinctive black reproductive structures (apothecia) that measure 300–460 micrometres in diameter. The lichen grows primarily on tree bark, particularly on ash and oak trees in the United Kingdom, while in continental Europe it shows an altitudinal distribution pattern, occurring mainly in mountains in southern regions but across various elevations in Central Europe. It typically grows alongside other nitrogen-tolerant lichen species and can be identified by its response to specific chemical spot tests....read more on Wikipedia.