tLecanora muralis (Schreb.) Rabenh. is a ubiquitous epilithic crustose lichen of the temperate climate. Itis well studied in terms of diel and annual carbon budget and productivity with continuous long-termobservations in the field in 1995/96 by Otto L. Lange, Würzburg, and collaborators. However, these ear-lier studies left open the question to which extent the lichen is desiccation tolerant and if desiccationtolerance might possibly limit photosynthetic activity. In present study measurements of chlorophyllfluorescence parameters were performed to assess photosynthetic activity under various daily weatherconditions throughout the year and recovery from desiccation after various periods of dryness in ambi-ent air. Under any weather conditions, including strong frost for several days with night-temperaturesaround −15◦C and strong heat of several days with day-temperatures around 35◦C, the lichen was fullyphotosynthetically competent after wetting the samples for 15 min by submersion in water when theywere dry in the field in the absence of actual incident precipitation. Chlorophyll fluorescence parame-ters were identical under all weather conditions sampled. A sample kept dry in ambient air for 37 daysshowed full recovery of chlorophyll fluorescence parameters after wetting for 30 min. Samples desic-cated for longer periods up to 155 days took longer wetting times of about 300 min and recovered onlypartially but nevertheless showed active photosynthetic electron transport. Of 17 samples desiccated for177–178 days only three recovered after rewetting for several days. It is concluded that the desiccationtolerance of L. muralis is sufficient to overcome dry spells of duration as it normally occurs in its naturalenvironment. Desiccation tolerance is not likely to limit carbon budget and productivity.