Through the combined use of molecular and microscopy techniques, the endolithic lichens Lecidea cancriformis and Lecidea sp. were identified, even in the absence of fruiting bodies, and positioned under epilithic lichens. Cells of both algal and fungal symbionts were observed in fissures and cracks of the lithic substrate with no clear heteromerous structure. At the ultrastructural level, the two lichens differed in terms of their algal-fungal relationships. Only one genotype of Trebouxia ITS sequence was identified from specimens of Lecidea sp., Umbilicaria aprina and Buellia frigida from the same zone, which could be mainly determined by low availability of alga in these extreme environments. These lichens showed features typical of both chasmoendolithic and euendolithic microorganisms. Signs of biogeophysical and biogeochemical action on the substrate were detected close to fungal cells. This action seemed to be mainly conditioned by the local physico-chemical features of the substrate. Evidence for the biomobilization of elements by these endolithic lichens was found. L. cancriformis was observed to accumulate substantial amounts of calcium-rich biominerals. The combined approach proposed is useful for mapping the distribution of endolithic lichens and analysing the processes that occur in their microscopic environment.
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