Caloplaca pusilla (A. Massal.) Zahlbr.

    Thallus rosette-shaped, 1-3 cm diam., margin characterized by small short lobes, serried, slightly palmate, convex, pleated, pruinose; sometimes cocarde-shaped, colours inconspicous, brown at the center (old specimen), cream at lobe base, margin yellow-orange, salmon to yellowish. Apothecia scattered all over the thallus (except margin), sessile and occasionnally stipitate, disc brown-orange, margin thin, concolourous or yellow-ochre. Ascospores polarilocular, slightly diamond-shaped, 11-14 x 5-7 µm. Photobiont : trebouxioide. All parts K+ purple. On hard limestone or calcareous stones of walls. Belongs to Caloplaca saxicola group, but differs by its well lobate margin and lobes distinct and pruinose; but the discrimination between the different taxa is still difficult and it is even more difficult to find coherence between classifications based on morphology and molecular markers.*