Difference in secondary compounds and chlorophylls between fibrils and main stems in the lichen Usnea longissima suggests different functional roles

Extract

Usnea is a species-rich and widespread lichenized fungal genus of well-lit parts of forest canopies (Motyka 1936, 1947; Clerc 1998). The bright greenish colour of these beard lichens reflects the presence of usnic acid in the cortex, which forms a thin, but dense sleeve around the trebouxioid photobiont in the outermost parts of the medulla. Usnic acid, a widely distributed dibenzofuran derivative produced by various mycobiont genera, strongly absorbs UV-B, but also the shortest PAR wavelengths (e.g. McEvoy et al. 2006, M. McEvoy, K. A. Solhaug and Y Gauslaa unpublished). Depending on species (Halonen et al. 1998), Usnea also contains a wide range of UV-B absorbing depsidones and depsides, though these are usually assumed to be confined to the medulla. Quantitative data on lichen compounds are rare in Usnea species, particularly with respect to the intrathalline variation.