MULTIPLE ORIGINS OF LICHEN SYMBIOSES IN FUNGI SUGGESTED BY SSU RDNA PHYLOGENY

Phylogenetic hypotheses provide a context for examining the evolution of heterotrophic lifestyles. The lichen lifestyle, which is the symbio tic association of fungi with algae, is found in various representativ es of Dicaryomycotina, both Ascomycetes and Basidiomycetes. A highly r esolved parsimony analysis of small subunit ribosomal DNA (SSU rDNA) s equences suggests at least five independent origins of the lichen habi t in disparate groups of Ascomycetes and Basidiomycetes. Because liche n associations arose from parasitic, mycorrhizal, or free-living sapro bic fungi, neither mutualism nor parasitism should be construed as end points in symbiont evolution.