PHYLOGENETIC DIVERSITY OF TRENTEPOHLIALEAN ALGAE ASSOCIATED WITH LICHEN-FORMING FUNGI(1).

Nearly one-fourth of the lichen-forming fungi associate with trentepohlialean algae, yet their genetic diversity remains unknown. Recent work focusing on free-living trentepohlialean algae has provided a phylogenetic context within which questions regarding the lichenization of these algae can be asked. Here, we concentrated our sampling on trentepohlialean algae from lichens producing a diversity of growth forms (fruticose and crustose) over a broad geographic substratum, ecological, and phylogenetic range. We have demonstrated that there is no evidence for a single clade of strictly lichenized algae; rather, a wide range demonstrated the ability to associate with lichenized fungi. Variation was also observed among trentepohlialean algae in lichens from a single geographic area and tree, suggesting that fungi in close proximity can associate with different trentepohlialean algae, consistent with the findings of trebouxiophycean algae and cyanobacteria.

Fungi evolved right on track.

Dating of fungal divergences with molecular clocks thus far has yielded highly inconsistent results. The origin of fungi was estimated at between 660 million and up to 2.15 billion y ago, and the divergence of the two major lineages of higher fungi, Ascomycota and Basidiomycota, at between 390 million y and up to 1.5 billion y ago. Assuming that these inconsistencies stem from various causes, we reassessed the systematic placement of the most important fungal fossil, Paleopyrenomycites, and recalibrated internally unconstrained, published molecular clock trees by applying uniform calibration points. As a result the origin of fungi was re-estimated at between 760 million and 1.06 billion y ago and the origin of the Ascomycota at 500-650 million y ago. These dates are much more consistent than previous estimates, even if based on the same phylogenies and molecular clock trees, and they are also much better in line with the fossil record of fungi and plants and the ecological interdependence between filamentous fungi and land plants. Our results do not provide evidence to suggest the existence of ancient protolichens as an alternative to explain the ecology of early terrestrial fungi in the absence of land plants.