Molecular phylogeny of truffles (Pezizales : Terfeziaceae, Tuberaceae) derived from nuclear rDNA sequence analysis

Extensive morphological convergence or divergence, a common occurrence in f ungi, tends to obscure recognition of phylogenetic relationships among Pezi zales, widespread filamentous Ascomycetes with either enclosed underground (hypogeous) or exposed (epigeous) fruit bodies, that often establish mutual istic interactions with arboreous plants. Focusing on hypogeous Pezizales c ommonly known. as truffles, we sequenced the 18S rDNA from nine species bel onging to three different families (Tuberaceae, Terfeziaceae, and Balsamiac eae). A data set consisting of 1700 secondary structure-aligned sites, incl uding 24 homologous sequences from the GenBank DNA database and using three reconstruction methods, was employed to infer phylogenies in an interval r anging from the subordinal to the subgeneric level. As revealed by the 185 phylogenetic scheme, Balsamiaceae represent a monophyletic clade, comprisin g the hypogeous taxa Balsamia and Barssia, nested within Helvellaceae. Simi larly, the terfeziacean genera Pachyphloeus and Terfezia constitute togethe r with Cazia a distinct hypogeous clade nested within Pezizaceae, The lack of clustering between Terfezia arenaria and Terfezia terfezioides strongly supports the reassignnent of the latter taxon to the original monotypic gen us Mattirolomyces. Within Tuberaceae, which are sister to the highly evolve d Helvellaceae, the genus Tuber cannot be considered monophyletic if Choiro myces is recognized. The paraphyly of Tuber and other relationships that we re not supported by high bootstrap values, nor corroborated by morphologica l evidence, were supported by a parallel analysis of the faster evolving in ternal transcribed spacer (ITS) rDNA Distinct episodes of fruit body morpho logy shifts are discernable in the 185 rDNA phylogenetic tree. In all cases , the shift from an epigeous to a hypogeous form is the most parsimonious i nterpretation of character transformation, without any instance of characte r reversal. (C) 1999 Academic Press.