This volume provides an image-rich documentation of the morphology and ultrastructure of Eunotia species from southeastern Brazil, including description of new taxa and restudy of some original materials. Moreover, it represents the fi rst combination of taxonomic and ecological approaches to the study of Eunotia in tropical and subtropical regions. The materials studied included samples from distinct habitats (planktonic, periphytic and surface sediment) collected from 32 reservoirs of southeastern Brazil. Eighty-seven Eunotia species are illustrated with light and scanning electron microscopy on 108 plates and compared with other similar taxa. Among these, 13 taxa are reported here for the first time in Brazil, and 15 new taxa are described. Morphometric features of all taxa are described and compared with data from the literature. The ecological preferences (optima) of 19 taxa were calculated for nutrients (total phosphorus and total nitrogen), pH and conductivity. A comprehensive sample table with reservoirs, drainage basins, geographic coordinates and herbarium numbers as well as an extensive reference list complete the volume.The results of this work confirm the ecological preference of the genus for clean waters (ultraoligo- to mesotrophic). Two species (E. rhomboidea Hustedt and Eunotia maconi sp. nov.) were associated with eutrophic waters. This survey of Eunotia species from southeastern Brazil is of general interest to all readers working on diatoms. ukryj opis