An interesting hyphomycetous taxon was collected on submerged wood in a freshwater stream in Trat Province, Thailand. It is morphologically similar to endophragmiella-like taxa, characterized by macronematous, mononematous conidiophores, monoblastic, enteroblastic conidiogenous cells and clavate to obovoid, septate brown conidia. The unique feature of this taxon is that the mature conidium often bears a young new conidial primordium which develops percurrently from a lower semi-transparent cell and they secede simultaneously. Phylogenetic analyses of a combined LSU, SSU and RPB2 sequence data support the placement of this fungus together with Platytrachelon and close to the family Papulosaceae within Diaporthomycetidae, Sordariomycetes. A new genus is introduced to accommodate the new taxon as Aquimonospora. The novel species Aquimonospora tratensis is described and illustrated and is compared with other morphologically similar taxa.