Lecania atrynoides M. Knowles

    Thallus crustose, often discontinuous and fragmented, granular, rimose to areolate, surface smooth to cracked, dull whitish, greyish to pale brownish, prothallus hardly visible with sometimes pale sections contiguous to dark sections owing to invasive dark hyphae of other commensalistic fungi suggesting a prothallus. Apothecia abundant, 0.3-1 mm diam., more or less regular, scattered all over the thallus, disc flat to slightly convex, without pruine, dark brown-red to blackish, brown-green spots when moist and black when dry (using magnifying lens), exciple excluded when mature, concolourous or paler. Ascospores ellipsoid, 0-1-2-septate, 10-14 x 4,5-6 µm. Chemical spot tests negative. Photobiont: Chlorococcoid. Rather common, in crevices or below overhangs of exposed siliceous rocks in the xeric supralittoral zone, often at the highest level of Verrucaria (Hydropunctaria) maura. See Catillaria lenticularis, calcicolous and of which ascospores are different.

See also Catillaria chalybeia that differs by its conspicuous prothallus, metal-tinged. N.B. Highly variable species, several morphotypes may coexist in the same area. This species is also very close to Lecanora helicopis (sometimes named Lecania helicopis !), both sharing the same habitat. On weakly acid or slightly calcareous sea rocks there seems to be a particular form, see Lecania atrynoides forme maritime des roches calcaires.