Phylogeny of Discomycetes and early radiations of the filamentous ascomycetes inferred from 18SrDNA sequence data

The apothecial ascomycetes or cup fungi (Discomycetes sensu Korf, 1973) have open fruiting bodies or apothecia, and this group includes both lichenized and non-lichenized fungi. Analyses of ca 1600 aligned bp of 18S rDNA suggest that the apothecial ascomycetes radiated after the split between the ascomycete yeasts and the filamentous fungi. Though they may not be a monophyletic assemblage, they may be basal to other groups of filamentous ascomycetes and they clearly do not fit in with either the classes of fungi with flask-shaped fruiting bodies (Pyrenomycetes sensu Muller and von Arx, 1973) nor those with closed fruiting bodies (Plectomycetes sensu Fennell, 1973). Below the rank of class the orders Pezizales, Leotiales, Caliciales, and Lecanorales cannot be supported as monophyletic groups by this analysis of fungal representatives.;I designed primers for the polymerase chain reaction (PCR) which amplify specifically the fungal nuclear 18S rDNA from both lichenized and non-lichenized fungi but do not amplify green-algal rDNA. With these primers I sequenced the 18S rDNA from representatives of ten fungal genera from four orders: Pezizales (Ascobolus, Morchella, Peziza), Leotiales (Leotia, Sclerotinia), Caliciales (Calicium, Mycocalicium, Sphaerophorus), and Lecanorales (Lecanora, Lecidea), within the Discomycetes. (Calicium, Sphaerophorus, Lecanora, and Lecidea are lichenized fungi).;The apothecial ascomycetes sequenced have had a slower rate of molecular change overall than that seen in the Plectomycetes, Pyrenomycetes or some ascomycete yeasts. Mycocalicium, Lecanora, Lecidea and Calicium have 18S genes larger than the expected 1.8 kb (up to an extra 1.4 kb) because of the presence of between one and eight insertions in each.