PHYLOGENETIC-RELATIONSHIPS AMONG ASCOMYCETOUS TRUFFLES AND THE TRUE AND FALSE MORELS INFERRED FROM 18S AND 28S RIBOSOMAL DNA-SEQUENCE ANALYSIS

Phylogenetic relationships among ascomycetous truffles and the true an d false morels were examined by using sequences from two nuclear encod ed ribosomal DNA genes. The data consist of 18S rDNA and partial 28S r DNA sequences for 29 taxa. Individual and combined data sets were anal yzed by maximum parsimony (MP), neighbor-joining (NJ) and maximum like lihood (ML) methods. Parsimony analysis of the combined data set, whic h contained 3 published 18S sequences and consisted of 2358 nucleotide characters, yielded a single most parsimonious tree of 1728 steps. Th e results indicate that the hypogeous ascomycetous truffle and truffle like taxa studied represent at least 5 independent lineages within the Pezizales. Results also suggest that several epigeous and most hypoge ous taxa have been misplaced taxonomically. Bootstrap analyses show st rong support for a Tuberaceae-Helvellaceae clade which is a monophylet ic sister group of a Morchellaceae-Discinaceae clade. Rhizina is a sis ter group to both of these clades in the MP and ML trees while in the NJ tree it is a sister of the Morchellaceae-Discinaceae clade. MP, ML, and NJ tree topologies indicate that Rhizina should be removed from t he Helvellaceae and classified in a monotypic family, the Rhizinaceae. A phylogenetically-based classification for these fungi is proposed t ogether with emendations of 4 families.