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 and false morels were examined by using sequences from two nuclear encoded ribosomal DNA genes. The data consist of 18S rDNA and partial 28S rDNA sequences for 29 taxa. Individual and combined data sets were analyzed by maximum parsimony (MP), neighbor-joining (NJ) and maximum likelihood (ML) methods. Parsimony analysis of the combined data set, which contained 3 published 18S sequences and consisted of 2358 nucleotide characters, yielded a single most parsimonious tree of 1728 steps. The results indicate that the hypogeous ascomycetous truffle and trufflelike taxa studied represent at least 5 independent lineages within the Pezizales. Results also suggest that several epigeous and most hypogeous taxa have been misplaced taxonomically. Bootstrap analyses show strong support for a Tuberaceae-Helvellaceae clade which is a monophyletic sister group of a Morchellaceae-Discinaceae clade. Rhizina is a sister 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 the Helvellaceae and classified in a monotypic family, the Rhizinaceae. A phylogenetically-based classification for these fungi is proposed together with emendations of 4 families.