A new freshwater ascomycete Micropeltopsis quinquecladiopsis sp. nov. was collected on submerged twigs in a stream in Thailand. The fungus is described at the light microscope, scanning and transmission electron microscope level. Distinctive features are the appendaged 1-septate hyaline ascospores. The appendage arises as an outgrowth of the episporium from a basal stalk, then divides into five arms (three long and two short). The episporium and appendages are surrounded by an indistinct (at light microscope level) mucilaginous layer. The fungus is assigned to the Dothideales (Trichothyriaceae). Ascospore appendage ontogeny is compared with those of marine Ascomycota (Halosphaeriales).