Bacidia rubella (Hoffm.) A. Massal.

Bacidia rubella is a species of corticolous (bark-dwelling), crustose lichen in the family Ramalinaceae. First described in 1796, it features a grey to yellow-green thallus with small granular structures covering its surface. When present, its distinctive fruiting bodies (apothecia) range from pale to dark red-brown in colour, measuring up to 1 mm in diameter. The species occurs widely throughout Britain and Ireland and is also broadly distributed across lowland central and northern Europe, typically inhabiting nutrient-rich bark of mature trees such as maple, ash, and elm in parklands, roadsides, and fertile woodlands. It generally avoids heavily polluted areas and favours continental, montane habitats in the Mediterranean region. It is known to host several species of fungi that specifically colonise lichens.