Caloplaca crenulatella  (Nyl.) H. Olivier s. l.

    Thallus crustose, highly variable, well developed and demarcated or inconspicuous or even absent; if present, rarely areolate, areoles 0.2-0.5 mm across, pale yellow, yolk in well-lit areas but often dull yellow, grey-yellow tinged greenish in our prospection area and in shaded and humid areas (N.B. quite similar to the Protoblastenia rupestris thallus and possibly growing in combination). Apothecia scarce and scattered or less frequently numerous, sessile, 0.5-0.8 mm diam., disc flat to slightly convex, yellow to orange, exciple thick and distinct, seldom crenulate when mature, paler than the disc (in section within a KOH solution, rapidly desintegrated). Ascospores polarilocular, narrowly ellipsoid, apices pointed, thin septa, 1/7 to 1/5th of total length (1-3 µm and almost negligeable when observed in water), 13-23 x 5-8 µm. K+ purple. Rather rare in our prospection area, on calcareous rocks, much less frequently on concrete, mortar, abestos or fibre cement, notably in nutrient-rich wastelands or brownfields. N.B. This species, considered here as a complex, or sensu lato, is extremely variable and presents very different aspects according notably to its habitats. Rather easy to identify considering the ascospores characteristics althought several taxa share some of them... This explains why so many synonymous and related taxa have been described. See Caloplaca flavovirescens, Caloplaca holocarpa s.l., Caloplaca lactea, etc. with different ascospores.