Lepraria caesioalba (B. de Lesd.) J. R. Laundon

    Thallus most often forming small irregular rosettes, 1-4 cm diam., diffuse and with more or less delimited margins, prothallus absent, dull whitish, pale greyish, grey-bluish, purplish-gray, not powdery but composed of piles of minute granules, 0.1-0.2 mm diam., concolourous, becoming darker and blacken towards the center (often with a typical cockade shape). Apothecia unknown. Photobiont: green algae. Chemical spot tests variable: 5 chemotypes have been described, but most often C-, K+ yellowish and Pd+ orange.  Not especially maritime, rather common and in large colonies on humid and mossy siliceous rocks and walls or piles of rocks on the foreshore with other lichens.

N.B. Several taxa may share the same species name, but coastal specimen are much more developed and have a much more uneven surface than continental specimen found in the Ardennes that are evenly granulose (see pictures).

_ As for other Lepraria species, only the typical specimen may be identified without chemical reactions.