Catillaria lenticularis (Ach.) Th. Fr.

   Thallus crustose, highly variable notably on plane substratum, usually immersed, endolithic and inconspicuous, whitish or glaucous on well exposed limestone, or thin ochre-greyish, pale brown, ochre, olivaceous on shaded and moist calcareous rocks, prothallus not visible.  Apothecia usually numerous, 0.2-0.5 mm diam., regularly scattered, little prominent, plane at first then convex, dark red-brown to dark brown when moist, blackish when dry, margin concolourous or paler disappearing when old. Ascospores oblong or oblong-ellipsoid, 1-septate, 6-11 x 2-4 µm, paraphyses apices capitate with dark brown cap. Photobiont: Dictyochloropsis. Chemical spot tests negative. Prefers slightly nutrient-rich hard limestones and other highly calcareous rocks on or near Verrucaria sp of calcareous or alkaline rocks. See Catillaria chalybeia of which the thallus has copper tinge  and that is rarer on calcareous substrata.*