Systematics of the Pezizomycetes--the operculate discomycetes.

The Pezizomycetes (order Pezizales) is an early diverging lineage within the Pezizomycotina. A shared derived character, the operculate ascus, supports the Pezizales as monophyletic, although functional opercula have been lost in certain taxa. Phylogenetic relationships within Pezizales were studied using parsimony and Bayesian analyses of partial SSU and LSU rDNA sequences from 100 taxa representing 82 genera and 13 of the 15 families currently recognized. Three primary lineages are identified that more or less correspond to the A, B and C lineages resolved in previous analyses using SSU rDNA: (A) Ascobolaceae and Pezizaceae; (B) Discinaceae-Morchellaceae and Helvellaceae-Tuberaceae; (C) Ascodesmidaceae, Glaziellaceae, Pyronemataceae, Sarcoscyphaceae and Sarcosomataceae. In contrast the monotypic Rhizinaceae and Caloscyphaceae are resolved as two independent lineages. Bayesian analyses support a relationship among Rhizina and two species of Psilopezia (Pyronemataceae). Only lineage C is highly supported. The B and C lineages form a strongly supported monophyletic group. None of these lineages corresponds to earlier proposed suborders. The A and B lineages are supported by certain morphological features (e.g. ascus bluing reaction in iodine, cytology of spores and paraphyses, septal pore structures and excipulum structure); these characters have been subject to homoplasy. Lineage C is the largest and most heterogeneous, and no unifying morphological features support its recognition. The Pyronemataceae, in which almost half of the species in the order are found, is not monophyletic because the Ascodesmidaceae and Glaziellaceae are nested within it. The relationships among all families in the C lineage remain uncertain. The origin of various forms of ascomata, including hypogeous forms (truffles and truffle-like), epigeous cleistothecia, simple reduced apothecia and highly elaborate, stipitate forms (helvelloid and morchelloid), are discussed.