XVI International Botanical Congess

Symbiotic organisms, whether mutualistic or parasitic, are difficult to place within traditional classifications. This is especially true of fungi and algae in lichen symbioses, and fungi that parasitize them. Molecular tools allow us to examine relationships among symbionts. Phylogenetic analysis of 150 nuclear SSU rDNA sequences, supported by rDNA ITS and mitochondrial SSU rDNA data, suggest that lichenization occurs in three lineages of ascomycetes, the Sordariomycetes/Arthoniomycetes, Eurotiomycetes/Chaetothyriomycetes, and Lecanoromycetes. Fungal parasites of lichens also evolved in a number of ascomycete and basidiomycete groups, which may account for their parasitic differences. In contrast, some algal symbionts show little genotypic variation relative to that of their fungal partners, supporting the dispersal of symbiotic algae between different lichens.