Verrucaria rosula

Verrucaria rosula is a species of saxicolous (rock-dwelling), crustose lichen in the family Verrucariaceae. It is known from several European countries, including Britain and France. The lichen is characterised by its distinctive growth pattern, forming rosette-like patches that merge together as they develop—a feature that inspired its name rosula (meaning "little rose"). Its thallus varies from grey-green to brown, depending on light exposure, and features rounded reproductive structures with pale openings. V. rosula typically occurs on damp rocks and stones near streams or on water-saturated ground, where it grows alongside several other wetland lichen species....read more on Wikipedia.