Caloplaca thallincola (Wedd.) Du Rietz

    Thallus placodioid, forming in favourable conditions closely appressed, very regular, round cartwheels, 1-5 cm diam., with long and wide contiguous lobes, smooth and more or less pleated, with parallel furrows; margin made of slightly divided and palmate end-lobes. Colour, variable according to exposition, most often a magnificent bright golden-yellow to bright yellow-orange. Apothecia are generally numerous and rarely absent, often with a mixture of apothecia of different development, the most developed being grouped together towards the center where they can reach 0.3-0.8 mm in diameter, disc a little convex, Golden yellow darker or more brownish than the thallus, paler margin disappearing with age. Polarilocular spores, broadly elliptical, lemon-shaped or rhomboidal with a septum of 4-5 µm (1/3 to 1/2 of the total length of the spore), 11-14 x 8-11 µm according to the literature; 11-15 x 8-11 µm according to our measurements. Photobiont: trebouxioid. Branched or forked paraphyses with swollen ends. Thallus and apothecia K + purple.  Common on not too exposed siliceous rocks where this species is often overgrowing marine  Verrucaria and notably Verrucaria (Hydropunctaria) maura  of which it could be a parasite.  N.B. In the halophilic zone Caloplaca scopularis  notably more rare, is very similar but with less bright colours.*