The photosynthetic capacity changes that have previously been documented in lichens are reviewed together with the mechanisms of photosynthetic capacity change in free-living algae recently proposed by Prezelin and co-workers. Examination of seasonal capacity changes in Peltigera praetextata, P. rufescens, Cladonia rangiferina, C. stellaris, and Caloplaca trachyphylla using photosynthetic-illumination curves, provisionally establishes that synthesis of additional photosynthetic units, seasonal interruption of energy transduction, as well as enzymatic rate changes in the Calvin cycle, are all involved in these capacity changes.