Phylogenetics of Helotiales and Rhytismatales based on partial smallsubunit nuclear ribosomal DNA sequences

摘要

The evolutionary sequence leading to the differentiation of ascomatal and ascal types in the Euascomycetes remains poorly understood. To investigate the placement of the inoperculate discomycetes in the phylogeny of Euascomycetes, partial small subunit ribosomal DNA sequences for 36 species placed in Helotiales and Rhytismatales were combined with those of 54 additional species representing the major ascomycete lineages, and two basidiomycetes as outgroups. The apothecial orders Helodales, Rhytismatales, Pezizales, Caliciales, Lecanorales, and Peltigerales. were represented by multiple genera. Maximum parsimony recovered over 100 000 equally most parsimonious trees, with the strict consensus tree collapsing many inoperculate discomycetes. into a large Euascomycete polytomy. Weighted parsimony resolved a paraphyletic clade composed of Rhytismatales and Helotiales. Families grouping consistently in the Helotiales/Rhytismatales clade included Bulgariaceae, Helotiaceae, Hemiphacidiaceae, Leotiaceae, Loramycetaceae, Phacidiaceae, Rhytismataceae, Rutstroemiaceae, Sclerotiniaceae, and Thelebolaceae. Orbiliaceae did not group with Helotiales. The small subunit data matrix was more useful for familial relationships in Helotiales and Rhytismatales. Of families represented by multiple taxa, Sclerotiniaceae and Hemiphacidiaceae were monophyletic, Rhytismataceae was paraphyletic, and Helotiaceae and Phacidiaceae were polyphyletic. The placement of several inoperculate discomycete genera with historically problematic ordinal or familial placement based on morphological and developmental features remained equivocal in the small subunit phylogeny. These genera include Cyclaneusma, Darkera, Gremmeniella, Naemacyclus, Phacidium, and Piceomphale. Although further studies are needed, we use the small subunit phylogeny as a,framework for discussing the evolution of the ascoma and ascus, the delimitation between Helotiales and Rhytismatales, and certain family concepts within the inoperculate discomycetes.