Description of five new D.G.Mann (Bacillariophyta, Diadesmidaceae) species from Indonesia with comments on the morphological boundaries of the genus.

During a survey of the Indonesian diatoms, five D.G.Mann taxa that could not be identified, based on the available literature were discovered. Based on light microscopy, scanning electron microscope observations and comparisons with similar taxa, all of them are described as new species. All taxa were found on mosses growing on tree trunks and concrete on the islands of Banda Besar and Seram and from spring on Java Island. is most similar to and , but it can easily be distinguished from both taxa, based on the lower striae density, the narrower valves and the well-developed silica ridges on the valve face/mantle junction. resembles , but they can be easily distinguished, based on their valve widths and the direction of the grooves located on the distal and proximal raphe endings. is most similar to , and . Amongst all the species compared, is the only one with a highly asymmetrical central area, with the isolated pore located on the wider side. shares similarities with and , but it has a notably higher stria density. From , it can also be separated by the morphology of striae and the lack of ghost areolae in the central area. is unique in the whole genus due to the presence of multiple isolated pores.