Freshwater Dothideomycetes are a highly diverse group of fungi, which are mostly saprobic in freshwater habitats worldwide. They are important decomposers of submerged woody debris and leaves in water. In this paper, we outline the genera of freshwater Dothideomycetes with notes and keys to species. Based on multigene analyses and morphology, we introduce nine new genera, viz . Aquimassariosphaeria , Aquatospora , Aquihelicascus , Fusiformiseptata , Neohelicascus , Neojahnula , Pseudojahnula , Purpureofaciens , Submersispora ; 33 new species, viz . Acrocalymma bipolare , Aquimassariosphaeria kunmingensis , Aquatospora cylindrica , Aquihelicascus songkhlaensis , A. yunnanensis , Ascagilis submersa , A. thailandensis , Bambusicola aquatica , Caryospora submersa , Dictyocheirospora thailandica , Fusiformiseptata crocea , Helicosporium thailandense , Hongkongmyces aquaticus , Lentistoma aquaticum , Lentithecium kunmingense , Lindgomyces aquaticus , Longipedicellata aquatica , Neohelicascus submersus , Neohelicomyces dehongensis , N. thailandicus , Neohelicosporium submersum , Nigrograna aquatica , Occultibambusa kunmingensis , Parabambusicola aquatica , Pseudoasteromassaria aquatica , Pseudoastrosphaeriella aquatica , Pseudoxylomyces aquaticus , Purpureofaciens aquatica , Roussoella aquatica , Shrungabeeja aquatica , Submersispora variabilis , Tetraploa puzheheiensis , T. yunnanensis ; 16 new combinations, viz. Aquimassariosphaeria typhicola , Aquihelicascus thalassioideus , Ascagilis guttulaspora , A. queenslandica , A. seychellensis , A. sunyatsenii , Ernakulamia xishuangbannaensis , Neohelicascus aquaticus , N. chiangraiensis , N. egyptiacus , N. elaterascus , N. gallicus , N. unilocularis , N. uniseptatus , Neojahnula australiensis , Pseudojahnula potamophila ; 17 new geographical and habitat records, viz. Aliquandostipite khaoyaiensis , Aquastroma magniostiolata , Caryospora aquatica , C. quercus , Dendryphiella vinosa , Ernakulamia cochinensis , Fissuroma neoaggregatum , Helicotruncatum palmigenum , Jahnula rostrata , Neoroussoella bambusae , N. leucaenae , Occultibambusa pustula , Paramonodictys solitarius , Pleopunctum pseudoellipsoideum , Pseudocapulatispora longiappendiculata , Seriascoma didymosporum , Shrungabeeja vadirajensis and ten new collections from China and Thailand, viz. Amniculicola guttulata , Aquaphila albicans , Berkleasmium latisporum , Clohesyomyces aquaticus , Dictyocheirospora rotunda , Flabellascoma fusiforme , Pseudoastrosphaeriella bambusae , Pseudoxylomyces elegans , Tubeufia aquatica and T. cylindrothecia . Dendryphiella phitsanulokensis and Tubeufia roseohelicospora are synonymized with D. vinosa and T. tectonae , respectively. Six orders, 43 families and 145 genera which belong to freshwater Dothideomycetes are reviewed. Of these, 46 genera occur exclusively in freshwater habitats. A world map illustrates the distribution of freshwater Dothideomycetes.

Guizhou and Yunnan Provinces (Yungui Plateau) in Southwestern China are well known as biodiversity hotspots. We introduce two new species in this study viz., Mucispora hydei (in Fuscosporellaceae, Fuscosporellales, Sordariomycetes) and Tolypocladium cucullae (Ophiocordycipitaceae, Hypocreales, Sordariomycetes) and six new records based on morpho-molecular analyses. Full descriptions, color photographs and phylogenetic trees to indicate the placements of new species are provided.

Eight freshwater asexual strains collected from China and Thailand were subjected to morpho-molecular analyses. BLAST search results showed that the new strains belonged to Pleurotheciales, Sordariomycetes. Phylogenetic analyses based on a combined LSU, SSU, ITS and RPB2 sequence dataset are used to clarify the placement of the new strains within Pleurotheciales. Pleurothecium guttulatum and Pleurotheciella sympodia are introduced as two new species from freshwater habitats. New geographical record of Pleurotheciella nilotica from Asia (Thailand and China) is reported. New habitat and geographical records of Phaeoisaria annesophieae (from freshwater habitats in Asia) are reported. Descriptions and illustrations of the new species and records, as well as known species Rhexoacrodictys erecta and Phaeoisaria annesophieae, are provided. A key to Pleurotheciella species is provided.

During our ongoing surveys of fungi on submerged wood in the Greater Mekong Subregion, we collected two new species similar to Bactrodesmium longisporum. Pseudobactrodesmium gen. nov. is introduced to accommodate the new species, P. aquaticum, P. chiangmaiensis and B. longisporum is transferred to this genus. Fasciculate conidiophores, enteroblastic conidiogenous cells and subulate to fusiform, phragmoseptate conidia with a tapering apical cell and sheath characterize the genus. Pseudobactrodesmium aquaticum has longer conidia than P. chiangmaiensis. The placement of Pseudobactrodesmium in Dactylosporaceae (Eurotiomycetes) is a novel finding based on analyses of combined LSU, SSU, ITS and RPB2 sequence data. Our study reveals that Pseudobactrodesmium is likely to be a speciose genus with different species in streams around the world.