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Lichen associations arose several times within the fungi, yet until recently the closest relatives to lichen-forming fungi were not known. Molecular characters have allowed the comparison of fungi with diverse lifestyles and morphologies, and parsimony and maximum likelihood analyses of SSU rDNA sequences have been used to produce phylogenetic hypotheses of fungal relationships and to predict origins of the lichen habit. Analyses of two data sets, the first including 25 ascomycetous fungi, the second including 75 ascomycetous, basidiomycetous and zygomycetous fungi, with both parsimony and maximum likelihood analyses, suggested at least two lichen origins within the Ascomycetes, and at least three lichen origins within the Basidiomycetes. The optimum value for the transition to transversion ratio (T) for maximum likelihood analysis of the ascomycete dataset was 1.6. Topologies of trees from parsimony and maximum likelihood analyses had minor differences; maximum likelihood was found to be the most robust analysis. These phylogenetic analyses have led to refined hypotheses of relationships of lichen-forming fungi, and the derivation of a comprehensive phylogeny for the Eumycota.

The lichen habit is one of the most evolutionarily successful lifestyles in the Eumycota, the true fungi. Almost 1/5 of the 65,000 known fungal species form lichen associations with algae. Differences in lichen morphology and algal interactions suggest that these fungi are related to diverse groups of saprobic or parasitic fungi. By using the complete nucleotide sequences of the small subunit ribosomal DNA (SSU rDNA) from 75 fungi, including 10 that form lichen associations, we have examined the evolution of the lichen habit within a phylogenetic context. Our previous phylogenies produced with parsimony methods suggested that lichenization arose convergently and repeatedly in the Eumycota and in the Ascomycetes, and therefore, the lichen-forming fungi are polyphyletic. Reanalysis of this data set using maximum likelihood analysis has supported the polyphyly of the lichen habit. Topologies of trees from parsimony and maximum likelihood analyses had only three minor differences, none of which affected the number of lichen origins. Such resolved phylogenies are dependent on selecting taxa that represent the diversity of fungal lineages, and having nearly complete SSU rDNA sequences. Analysis of the dataset including only the 5-1150 nt produced hundreds of equally parsimonious trees that obscured the relationships among lichen-forming fungi, as did datasets lacking lichen-forming taxa or those with fewer discomycetes. Addition of SSU rDNA sequences from 31 other lichen-forming fungi clarified delimitation of the large order Lecanorales, to include Sphaerophoraceae, but to exclude Pertusariaceae and Umbilicariaceae. These analyses allowed placement of the obligately asexual Leprocaulon in the order Lecanorales, and Siphula and Thamnolia in an independent clade including other lichen-forming fungi such as Baeomyces, Dibaeis, Gyalecta, and Pertusaria. Also, we were able to phylogenetically identify fungal sequences associated with umbilicate Lichens buried under glaciers for thousands of years. As shown in our analyses, molecular systematics using SSU rDNA sequences can produce highly-resolved phylogenetic hypotheses for the Eumycota, the Ascomycetes and the Lecanorales, and provide further evidence for the multiple evolutionary origins of lichen symbioses.

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• Lichenized fungi of the genus Lepraria lack ascomata and conidiomata, and symbionts codisperse by soredia. Here, it is determined whether algal symbionts associated with Lepraria are monophyletic, and whether fungal and algal phylogenies are congruent, both of which are indicative of a long-term, continuous association between symbionts. • The internal transcribed spacer (ITS) and part of the actin type I locus were sequenced from algae associated with Lepraria, and the fungal ITS and mitochondrial small subunit (mtSSU) were sequenced from fungal symbionts. Phylogenetic analyses tested for monophyly of algal symbionts and congruence between algal and fungal phylogenies. • Algae associated with Lepraria were not monophyletic, and identical algae associated with different Lepraria individuals and species. Algal and fungal phylogenies were not congruent, suggesting a lack of strict codiversification. • This study suggests that associations between symbionts are not strictly maintained over evolutionary time. The ability to switch partners may provide benefits similar to genetic recombination, which may have helped this lineage persist. [ABSTRACT FROM AUTHOR]

An abstract of the article "Detection, Distribution, and Temperature-Dependent Growth of Geomyces destructans," by David Blehert et al is presented.