Lichen Allelopathy: A Review

Secondary metabolites produced by lichen-forming fungi have attracted attention of investigators for over 100 years. Approximately 500 compounds have been reported from lichens, of which about 350 appear to be unique. Most of these compounds are weak phenolic acids which are produced by the fungal partner and accumulate on the outer walls of fungal hyphae. Concentrations vary considerably within and among species; however, values of 1-2% air dry wt are commonly observed and values as high as 20% have been reported in some. Ecologists have long assumed an antibiotic role for these compounds, and recent evidence suggests that they play an important adaptive role defending lichen thalli from herbivores and pathogens; they also suppress neighboring lichen and moss competitors, and there is some evidence that they can inhibit higher plants. As such, they are allelochemicals in the broadest sense of the term.