Three new D.G.Mann (Bacillariophyta) species from Rapa Nui (Easter Island) found in terrestrial diatom assemblages dominated by widely distributed taxa.

Background: Rapa Nui (Easter Island = Isla de Pasqua) is of volcanic origin, best known for about 900 man-made stone statues known as . It is one of the most isolated inhabited islands on Earth and studies on the diatoms of Rapa Nui are very few.

Methods: Light (LM) and electron microscopic (SEM) observations of a single sample collected from Rapa Nui are presented. The samples (mix of soil and organic detritus) were collected from ground of cave entrance.

Results: The samples were characterized by low diatom diversity and strongly dominated by terrestrial (soil) forms. Among the taxa present in the material studied were cosmopolitan forms of the genera , , , , and . Whereas most of taxa of the enumerated genera were identifiable, only one among four species distinguished in the samples studied was identified. This taxon was . , a cosmopolitan species known previously from South America (Brazil) and Asia (China). The three remaining species could not be assigned to any established species. Therefore, based on external and internal morphological features from light and scanning electron microscopic analysis, we describe here three species new to science, including: . , . and . All three taxa new to science are compared to established species and their significance for the global distribution of the genus is discussed.