Lichens growing on moraines at Storbreen and Nigardsbreen, southwest Norway, were investigated. The mean of the five largest thalli is the optimum lichenometric index of the lichens growing in a quadrat of a given size. The variability of this index is closely related to the size of the quadrat, and decreases with increasing sampling area. Rhizocarpon alpicola is much more variable than species within the Section Rhizocarpon, although this may be due to the relatively young R. alpicola populations on the moraines that were examined. With increasing sampling area, the mean of the five largest thalli per quadrat approaches the single largest diameter, reflecting the population structure of the lichens growing on the moraines