Taxonomy and Systematics of and

The circumscription and composition of the are controversial and based on poorly sampled or unsupported phylogenies. The generic limits within the hyaloscyphoid fungi are also very poorly understood. To address this issue, a robust five-gene Bayesian phylogeny (LSU, , , , mtSSU; 5521 bp) with a focus on the core group of and is presented here, with comparative morphological and histochemical characters. A wide representative sampling of supports it as monophyletic and shows (subgenus ) to be a strongly supported sister taxon. Reinforced by distinguishing morphological features, is here recognised as a separate genus, comprising , , and (previously treated in ). In a sister group to the - clade a new genus, , is created for three seldom collected and poorly understood species, , () and , previously treated in , and , respectively. The is polyphyletic, because forms a monophyletic group with , distant to and ; in addition, represents an early diverging lineage in s.str. The hyphae originating from the base of the apothecia in are considered anchoring hyphae (vs a subiculum) and is excluded from . A new genus, , is established to accommodate and , originally described in and are distinguished among hyaloscyphoid fungi by long tapering multiseptate hairs that are not dextrinoid or glassy, in combination with ectal excipulum cells with deep amyloid nodules. Unique to is cyanophilous resinous content in the hairs concentrated at the apex and septa. Small intensely amyloid nodules in the hairs are furthermore characteristic for and . To elucidate species limits and diversity in , mainly from Northern Europe, we applied genealogical concordance phylogenetic species recognition (GCPSR) using analyses of individual datasets (ITS, LSU, , , ) and comparative morphology. Eight species were identified as highly supported and reciprocally monophyletic. Four of these are newly discovered species, with two formally described here, viz. and . In addition, , which completely lacks prominent hairs, is here combined in , widening the concept of the genus. Numerous publicly available sequences named represent and the confusion between these two species is clarified. An additional four singletons are considered to be distinct species, because they were genetically divergent from their sisters. A highly supported five-gene phylogeny of identified four major clades in , with as a sister group. Two of the clades include species with a strong connection to bryophytes; the third clade includes species growing on bulky woody substrates and with pigmented exudates on the hairs; and the fourth clade species with hyaline exudates growing on both bryophytes and hardwood. A morphological account is given of the composition of and , including new observations on vital and histochemical characters. : Kosonen T, Huhtinen S, Hansen K. 2021. Taxonomy and systematics of Hyaloscyphaceae and Arachnopezizaceae. Persoonia 46: 26-62. https://doi.org/10.3767/persoonia.2021.46.02.