A three-gene phylogeny supports taxonomic rearrangements in the family Didymiaceae (Myxomycetes)

Myxomycetes, or plasmodial slime molds, are a monophyletic group of amoeboid protists whose classification is based mainly on morphological features of fruiting bodies. Although published phylogenies based on one or two genetic markers have clarified the boundaries of the main order-level systematic groups, the position and composition of some families and genera of myxomycetes are still a topic for discussion. In this study, we reconstructed the phylogeny of the family Didymiaceae based on three independent genetic markers: the 18S rDNA gene, the translation elongation factor 1-alpha, and the cytochrome c oxidase subunit 1 gene. Maximum likelihood and Bayesian inference phylogenetic analyses produced congruent topologies and showed that of the five major genera of the family, only species of the genus Diachea form a monophyletic clade, while the other four genera are clearly para- or polyphyletic. Species of the genus Didymium form a monophyletic clade with the only species of the genus Mucilago. The polymorphic species Lepidoderma tigrinum is clearly placed among 13 species of Diderma, including the type species of the genus. All other studied species of Lepidoderma form a separate clade together with Diderma fallax. We thus extend the latest nomenclatural revisions by disbanding the genera Mucilago and Lepidoderma, whereby the single species of Mucilago is transferred to the genus Didymium and L. tigrinum to Diderma. Extended taxon sampling allows the transfer of more nivicolous species of the former genus Lepidoderma to Polyschismium.