Bagliettoa calciseda (DC) Gueidan & Cl. Roux

    Thallus endolithic, whitish to pale greyish, smooth or minutely rugose with calcite crystals visible under magnifying lens, often dotted with tiny dark grey to grey-brownish fungi and lichenicolous cyanobacteria, on typical samples very minute black cracks radiating from perithecia may be observed; in addition, prothallus thin, black, frequently absent. Perithecia numerous, globose, 0.2-0.3 mm diam., black, involucrellum absent, completely immersed at the bottom of a small hole, 0.2-0.4  mm diam., persistent after lichen decay and producing a characteristic punched rocky surface, recently occupied holes still black during the progressive erosion of perithecia until their base is conserved. Ascospores colourless, ellipsoid, often distorted and subject to necrosis (visible as black spots or optical artefacts suggesting ascospores ornamentation), 23-28 x 10-13 µm. Photobiont: green algae. This species is common on hard limestone and easily perceptible owing to the minute holes riddling the rock surface, but most often these holes are empty or only accomodate altered perithecia, entailing difficult identification as well as hard separation from close species. Not to be confused with Verrucaria hochstetteri that may coexist within the same habitat but with much larger ascospores, 29-35 x 16-20 µm (in case exploitable perithecia are absent, identification rely on hole size, 0.4-0.7 mm diam for the latter). Not to be confused with Verrucaria baldensis of which the sooty section of perithecia is restricted to the apices and the bottom of holes is still whitish during the partial fall of perithecia.