| Summary: | Abstract: During a survey of the freshwater diatom fl ora of Ascencion Island, a small isolated volcanic island in the southern Atlantic Ocean, two diatom taxa that could not be identifi ed using the currently available literature were observed. Detailed light and scanning electron microscopy observations revealed that both taxa should be described as new species: Navicula ascensionensis sp. nov. and Eunotia meridioatlantica sp. nov. Both taxa are illustrated and compared to similar taxa worldwide. Navicula ascensionensis sp. nov. belongs to the Alineae section of the genus Navicula and can be distinguished from similar taxa by a combination of its valve dimensions, stria orientation and clearly curved proximal raphe endings. Eunotia meridioatlantica sp. nov. is distinguishable by its valve shape and shape of the broadly rounded, only very weakly protracted apices.
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