Life history and systematics of the aquatic discomycete Mitrula (Helotiales, Ascomycota) based on cultural, morphological, and molecular studies

Abstract

Mitrula species represent a group of aquatic discomycetes with uncertain position in the Helotiales and an unknown life history. Mitrula species were studied using a combination of cultural, morphological, and molecular techniques. Pure colonies were isolated from Mitrula elegans, and conidia were induced in vitro. Herbarium materials from Europe, Asia, and North America were studied. Sequences of rDNA, including partial small subunit rDNA, large subunit DNA and ITS, were used to infer phylogenetic relationships both within Mitrula and between Mitrula and other inoperculate discomycetes, with special attention to fungi that resemble Mitrula in morphology or ecology. Equally weighted parsimony analyses, likelihood analyses, constrained parsimony analyses, and Bayesian analyses were performed. Results suggest that (1) the anamorph of M. elegans produces brown bicellular conidia, (2) a new subalpine species M. brevispora is distinct, (3) more than six lineages and clades can be recognized in Mitrula, (4) the morphological species M. elegans is not monophyletic, (5) a close relationship between Mitrula and either Geoglossaceae or Sclerotiniaceae is not supported, (6) the Helotiaceae is paraphyletic, and (7) Mitrula belongs to a clade within the Helotiales that also includes other aero-aquatic genera, Cudoniella, Hydrocina, Vibrissea, Ombrophila, and Hymenoscyphus.