Hydropunctaria amphibia (Clemente) Cl. Roux

    Thallus moderately thick, smooth, glossy (notably when compared to similar species), dark green-bottle when moist, otherwise dark brown-blackish, black, slightly cracked and crazed in places, covered notably towards margin with small sinuous black wrinkles, radially ordered like fingerprints, center covered either with wrinkles and crests but oriented in all directions. No prothallus (or very seldom) determining a very delimited edge of the thallus. Perithecia numerous, large, conical-hemispherical, prominent and projecting up to 0.2-0.4 mm, apex typically plane and crenulate, irregular and damaged-like, ostioles visible as a minute pits. Ascospores simple, narrowly ellipsoid, 15-18 x 5-7 µm, (13-18 x 6-7 according to our measures). This species has 'thermophile' trends, preferentially on vertical walls of well-lit rocks in the Verrucaria (hydropunctaria) maura zone (or just below), the latter, much more common, differing from Hydropunctaria amphibia by its thallus, not glossy or matt, without wrinkles and crests and solely dots on the thallus, its perithecia, flat and smooth, ascospores larger. Verrucaria (Wahlenbergiella) striatula grows below on the foreshore and its ascospores are smaller. Many intermediare specimen can be found and discrimination between them requires ascospores observation (this is a minimum requirement). See also Verrucaria ditmarsica / erichsenii  which are also subject to different interpretations and grow higher on the foreshore. N.B. Not to be confused with  Hydropunctaria oceanica of which the thallus is thinner and perithecia smaller, more conical and ascospores larger and similar to those of  Hydropunctaria maura. In Mediterranean areas see also Hydropunctaria amphibia  Mediterranean taxon not ribbed and not subjected to tides. Some other forms growing at lower level might also be found: Hydropunctaria amphibia forma, with a thinner thallus and margins lace-like. Easily confused with Verrucaria (Wahlenbergiella) striatula that shares the same habitat.