Verrucaria marinomuralis Harada
Thallus superficial, thin, rimose, more or less cracked, pale grey to grey-greenish when moist, dull whitish to pale brownish when dry, prothallus unseen. Perithecia numerous, one or two third immersed, dome-shaped, seldom hemispherical, 0.3-0.5 mm diam., dark brown to blackish, rough, ostiole tiny and hardly visible, involucrellum blackish, extanding more or less sidelong, paraphyses more or less branched. Ascii 8-spored, clavate, 60-75 x 20-25 µm according to literature, 80-90 x 20-25 µm according to our measures, with 8 spores. Ascospores simple, hyaline, ellipsoid, 15-25 x 8-11 µm according to literature, 20-26 x 8-11 µm according to our measures. One of the few species growing on siliceous rocks in the seaspray zone (together or above Hydropunctaria maura). Differs from Verrucaria muralis by its habitat on acid rocks of the foreshore and slightly larger perithecia.
BREUSS O. A European record of Verrucaria marinomuralis (lichenised Ascomycetes, Verrucariales). Osterr. Z. Pilzk. 21. (2012).
Breuss focused his study on samples collected in Landevennec (site of our samples), but he was unable to compare his samples to the type, collected in Japan, using molecular tools. This explains why here we cannot confirm with certainty that this is the same species ss. str., because Japan is far from Brittany... This "species" V. m. Harada should, in all likehood, be brought closer of Verrucaria internigrescens, that presents the same specific and habitat characteristics.