Resumo
The results of the floristic study of epilithic diatoms from the upper course of the rio das Antas, state of Rio Grande do Sul, Brazil, are presented. The samples were taken monthly from July 2005 to February 2006, in four sites between 1030 and 1005 m alt. Thirty-eight species distributed in twenty-five genera and sixteen families are presented and illustrated. Most species are cosmopolitan, but we found some taxa with preference for, however not restricted to, oligotrophic and/or high altitude environments, such as Cocconeis placentula var. acuta, Meridion circulare var. constrictum and Psammothidium subatomoides. Gomphonema tenuissimum, Luticola costei and Pinnularia parvulissima are new citations for Rio Grande do Sul State, and the first was registered in scanning electron microscopy (SEM).
