Six species and four varieties of Diatoma (D. hiemale (Roth) Heib. , D. maximum (Grun.) Fricke, D. mesodon (Ehr.) Kuetz. , D. moniliforme Kuetz. , D. tenue Ag., D. vulgare Bory and its varieties) were studied using optical microscope and scanning electron microscope. Their taxonomic problems were discussed as well.