Ecological and taxonomic characterisation of Trentepohlia umbrina (Kützing) Bornet growing on stone surfaces in Lazio (Italy)

Purpose: The colonisation of building material by photosynthetic organisms is highly dependent on the environmental conditions and the nature of the substrate. The growths of red-orange phototrophic biofilms have been widely reported in the literature and have commonly been associated with the order Trentepohliales, whose ecological and taxonomical information needs to be improved. Considering the recurrent presence of such biofilms throughout the Lazio region, we would identify the occurring species and define their favourable environmental conditions, through morphological, genetic and ecological analyses. Results: Biofilms were collected across an altitude range of 0 to 860 m asl, occurring from the coast to 60-km inland. A dominant presence of the filamentous terrestrial green alga Trentepohlia umbrina (Kützing) Bornet was confirmed in all sites sometimes mixed with cyanobacteria of the genus Gloeocapsa. The distribution of Trentepohliales is generally given as pan-tropical, but some species, such as T. umbrina, are also distributed in temperate climates. Here, it is reported for the first time a Mediterranean occurrence of the species. Low humidity and light conditions, such as those occurring on vertical surfaces with mainly northern aspects, are the preferred environmental conditions. Coastal areas were more favourable for its growth, probably due to the higher nocturnal condensation that occurs here. Concrete and mortars were particularly bioreceptive to T. umbrina, but marble and trachyte were also colonised under favourable conditions. Conclusions: The findings better define the ecological range of this species, suggesting a wider biogeographic distribution, and adding information on morphological features and genetic data.