Rinodina immersa (Körb.) J. Steiner

   Endolithic crustose thallus difficult to observe, pale greyish, dirty whitish. Very numerous apothecia immersed in a well dug in the substrate and leaving an empty cupule when they disappear, 0.2-0.8 mm in diameter, flat to slightly convex disc, not pruinose, blackish, clean brownish edge, persistent, sometimes more or less lined with a pseudo whitish thalline edge. Hymenium without oil drops. Spores 1-septate, brown, of the bischoffi type with a wide equatorial band. 16-22 x 9-13 µm according to the literature, 15-20 x 9-13 µm according to our measurements. Colorless bacilliform conidia, 4 x 1 µm. Photobiont: green algae other than Trentepohlia. No significant colored chemical reactions. A slightly thermophilic saxicolous species growing on horizontal or slightly inclined calcareous rocks.

N.B. Appearance of a calcareous saxicolous Verrucaria but which have perithecia and not apothecia.

_  Species easily confused with Clauzadea immersa but the latter species has large and often powdery apothecia and simple colorless spores.