Halotthiaceae fam. nov. (Pleosporales) accommodates the new genus Phaeoseptum and several other aquatic genera.

During survey of freshwater fungi in Haute Garonne in the Pyrenees (southern France), we collected a remarkable species that is most comparable to the maritime fungus Mauritiana rhizophorae. The maritime genera Halotthia, Pontoporeia and Mauritiana as well as our newly collected species form a monophyletic clade in phylograms generated from LSU rDNA sequence analyses. This clade has undetermined familial status, and our new species is not congeneric with Halotthia, Pontoporeia or Mauritiana. A new monotypic genus, Phaeoseptum (represented by Ph. aquaticum sp. nov), therefore is introduced to accommodate the newly collected freshwater taxon. A new family, Halotthiaceae, is introduced to accommodate the four aquatic genera Halotthia, Mauritiana, Phaeoseptum and Pontoporeia.