XVI International Botanical Congess

The lichen-forming fungi pose challenges for the systematist at a variety of levels of the taxonomic hierarchy. At the ordinal level integration with other nutritional groups of fungi has developed rapidly in recent years, with molecular data providing a valuable test for and almost entirely supporting systems proposed on the basis of ascoma ontogeny and ascus structure. At the generic level cases where the same genus can include lichen-forming, non-lichen-forming and (or) lichenicolous species are increasingly being recognized, and in some cases the biology of a single species chan change during its life-cycle. The delimitation of genera does not only pose biological and conceptual problems, as there has been intense controversy as to whether lichen-forming genera should be separated on the basis of characters which result from the thalli formed or restricted to those of the fungus itself. Most exciting are the challenges at the species and population biology level. Does molecular data support the recognition of chemotypes? What are the limits of morphological variation in a species? What are the frequencies and implications of mechanical and sexual hybrids for the systematist? We now know that genotypically different fungal partners may be present in a single thallus, and ecological and geographical specialization with single species is starting to be analyzed with fascinating results.