Verrucaria hochstetteri Fr.

    Thallus endolithic, smooth, potentially creating an undulation-like aspect, without cracks, whitish, white-greyish, prothallus absent or very seldom black. Perithecia very numerous, completely immersed in pits, without projection over the thallus surface (ostioles appear flat under magnification lens), subspherical, 0.4-0.8 mm diam., involucrellum absent, a transversal section shows a continuous black wall all over the pit surface. Ascospores ellipsoid to broadly ellipsoid, perispore often present with sometimes a distinct fine ornamentation of short ridges, 29-34 x 16-20 µm. Extremely rare in our prospection area, on hard calcareous rocks where it is characterized by the numerous pits left. N.B. Identification of this species on the field is rather difficult and most often sampling is required in order to observe the perithecia and ascospores so that confusion with other species may be avoided. Unfortunately, old holes generally are empty. Not to be confused with Bagliettoa calciseda that may thrive in the same habitat but with smaller ascospores and in case of ascospore absence smaller holes, 0.2-0.4 mm diam. may contribute to identification.