Arthonia atlantica

Thallus effuse (spread out and flattened) or forming mosaics with other lichens. White to pale grey, matt, cracked-areolate (crazy-paving like). Apothecia more or less immersed in the thallus, irregulalry rounded (to 0.2mm dia) though more usually elongate or stellate, often joining to form an irregular reticulum (network).