Families and genera assigned to Tremellomycetes have been mainly circumscribed by morphology and for the yeasts also by biochemical and physiological characteristics. This phenotype-based classification is largely in conflict with molecular phylogenetic analyses. Here a phylogenetic classification framework for the Tremellomycetes is proposed based on the results of phylogenetic analyses from a seven-genes dataset covering the majority of tremellomycetous yeasts and closely related filamentous taxa. Circumscriptions of the taxonomic units at the order, family and genus levels recognised were quantitatively assessed using the phylogenetic rank boundary optimisation (PRBO) and modified general mixed Yule coalescent (GMYC) tests. In addition, a comprehensive phylogenetic analysis on an expanded LSU rRNA (D1/D2 domains) gene sequence dataset covering as many as available teleomorphic and filamentous taxa within Tremellomycetes was performed to investigate the relationships between yeasts and filamentous taxa and to examine the stability of undersampled clades. Based on the results inferred from molecular data and morphological and physiochemical features, we propose an updated classification for the Tremellomycetes. We accept five orders, 17 families and 54 genera, including seven new families and 18 new genera. In addition, seven families and 17 genera are emended and one new species name and 185 new combinations are proposed. We propose to use the term pro tempore or pro tem. in abbreviation to indicate the species names that are temporarily maintained.

Parmelioid lichens are a diverse and ubiquitous group of foliose lichens. Generic delimitation in parmelioid lichens has been in a state of flux since the late 1960s with the segregation of the large, heterogeneous genus Parmelia into numerous smaller genera. Recent molecular phylogenetic studies have demonstrated that some of these new genera were monophyletic, some were not, and others, previously believed to be unrelated, fell within single monophyletic groups, indicating the need for a revision of the generic delimitations. This study aims to give an overview of current knowledge of the major clades of all parmelioid lichens. For this, we assembled a dataset of 762 specimens, including 31 of 33 currently accepted parmelioid genera (and 63 of 84 accepted genera of Parmeliaceae). We performed maximum likelihood and Bayesian analyses of combined datasets including two, three and four loci. Based on these phylogenies and the correlation of morphological and chemical characters that characterize monophyletic groups, we accept 27 genera within nine main clades. We re‐circumscribe several genera and reduce Parmelaria to synonymy with Parmotrema. Emodomelanelia Divakar & A. Crespo is described as a new genus (type: E. masonii). Nipponoparmelia (Kurok.) K.H. Moon, Y. Ohmura & Kashiw. ex A. Crespo & al. is elevated to generic rank and 15 new combinations are proposed (in the genera Flavoparmelia, Parmotrema, Myelochroa, Melanelixia and Nipponoparmelia). A short discussion of the accepted genera is provided and remaining challenges and areas requiring additional taxon sampling are identified.

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Fungal mycoparasitism-fungi parasitizing other fungi-is a common lifestyle in some basal lineages of the basidiomycetes, particularly within the Tremellales. Relatively nonaggressive mycoparasitic fungi of this group are in general highly host specific, suggesting cospeciation as a plausible speciation mode in these associations. Species delimitation in the Tremellales is often challenging because morphological characters are scant. Host specificity is therefore a great aid to discriminate between species but appropriate species delimitation methods that account for actual diversity are needed to identify both specialist and generalist taxa and avoid inflating or underestimating diversity. We use the Biatoropsis-Usnea system to study factors inducing parasite diversification. We employ morphological, ecological, and molecular data-methods including genealogical concordance phylogenetic species recognition (GCPSR) and the general mixed Yule-coalescent (GMYC) model-to assess the diversity of fungi currently assigned to Biatoropsis usnearum. The degree of cospeciation in this association is assessed with two cophylogeny analysis tools (ParaFit and Jane 4.0). Biatoropsis constitutes a species complex formed by at least seven different independent lineages and host switching is a prominent force driving speciation, particularly in host specialists. Combining ITS and nLSU is recommended as barcode system in tremellalean fungi.

Recently, the number of cryptic species known has increased considerably, showing that species diversity has in many cases been underestimated in the past. Parmelia sulcata is a widely distributed species and one of the most common taxa in temperate Europe. The first intra-specific molecular studies on P. sulcata showed an unexpectedly high genetic variability. In the present work, we study the biodiversity of this taxon including specimens from four continents and using three molecular markers (nuITS, nuIGS rDNA, and partial β-tubulin gene). Two monophyletic groups of P. sulcata were encountered; one of these is epitypified as P. sulcata s. str and the other one is segregated as the new cryptic species P. encryptata sp. nov. Issues surrounding the lectotypification of Parmelia sulcata have also been elucidated.

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Four new lichenicolous Tremella species are described and characterized morphologically and molecularly. Tremella celata grows on Ramalina fraxinea, inducing the formation of inconspicuous galls, and having hyphae with incomplete clamps. Tremella endosporogena develops intrahymenially in the apothecia of Lecanora carpinea, having single-celled basidia and clampless hyphae. Tremella diederichiana is the name proposed for a species micromorphologically close to T. christiansenii but inducing the formation of small, pale galls on the thallus and apothecia of Lecidea aff. erythrophaea Tremella variae grows on Lecanora varia thallus, instead of on the apothecia, as do the other known Tremella species parasitizing Lecanora s.l. Phylogenetic relationships and host specificity of these species are investigated and compared with other taxa that show morphological resemblances, phylogenetic affinities or similar hosts. The formation of mitotic conidia inside old basidia (endospores), which is a poorly known reproductive strategy in the Basidiomycota, is also a distinctive character of Tremella endosporogena A discussion on the reproductive role and systematic implications of endospores is included.