Biocidal effect of lichen secondary metabolites against rock-dwelling microcolonial fungi, cyanobacteria and green algae

► (+)-usnic acid, norstictic acid and parietin inhibit in vitro the MCF growth. ► Cyanobacteria and green algae display sensibility only at high temperature (35 °C). ► Chromatic alteration caused by lichen metabolites to a white marble is negligible. ► Lichen metabolites are potential sources to control black patinas on stonework.