Buellia peregrina is described as new to science from small limestone pebbles on exposed ground of the coastal Namib Desert, Namibia. The species is unusual for two reasons: (1) it is the only species in Buellia s.l. currently known to grow euendolithically, i.e., establishing a thallus entirely within its rock substratum, and (2) its apothecia contain a previously unknown blue pigment, here described as peregrina-blue according to its colour and characteristic reactions with HNO3, KOH and HCl.

The anatomy of the endolithic, calcicolous lichen Verrucaria rubrocincta Breuss is described using optical and scanning electron microscopy. This lichen is locally abundant in caliche plates of open desert pavements in the Sonoran Desert of south-western Arizona. The endolithic growth of V. rubrocincta is distinctly layered. The upper layer is a fine-grained calcite (micrite). This layer is sparsely penetrated by hyphae and therefore cannot be interpreted as a lithocortex sensu stricto. Beneath the micrite is the photobiont layer. Below this photobiont layer hyphae form a pseudomedulla penetrating up to 1 cm into the caliche. Calcium oxalates occur in the pseudomedulla but are absent from uninhabited caliche. The analogy of a greenhouse describes the ecophysiological adaptations of this endolithic growth to the environmental extremes of the Sonoran Desert. The micrite acts as a roof and the photobiont layer and pseudomedulla represent the greenhouse interior. Verrucaria rubrocincta has thus evolved a strategy to successfully establish and survive within an extreme environment. Our study illustrates biodeterioration and biomineralization processes acting simultaneously within a single lichen species. Mineralogical evidence suggests that the micrite on the thallus surface is biologically induced. The hyphae of the lichen biodeteriorate the caliche thus forming the pseudomedulla. Simultaneously with this process micrite forms at the surface protecting the thallus from exposure and counter-balancing rock degradation. These combined effects of biodeterioration and biomineralization do not markedly accelerate erosion because inhabited and uninhabited areas of the same plate show similar surface heights.