A floristic study of Coscinodiscophyceae, Fragilariophyceae and Bacillariophyceae (Achnanthales) in the Ivaí, São João and Patos rivers from the upper Ivaí river basin, located at Prudentópolis, Paraná State, Brazil is presented. Forty-one samples were collected in March, June and July/2002 and January/2003, and analysed. Phytoplankton samples were collected with a plankton net (25 µm mesh); periphyton was collected by removing the attached material from submerged portions of aquatic macrophytes, rocks, sediment or the sandy substratum. Nine species of the class Coscinodiscophyceae, eight of the class Fragilariophyceae and fourteen of the order Achnanthales were identified. Thalassiosira weissflogii (Grunow) Fryxell & Hasle, Achnanthidium sp., Planothidium biporomum (Hohn & Hellerman) Lange-Bertalot and Cocconeis placentula var. pseudolineata Geitler were new diatom records for Paraná State.
Diatoms; algae; taxonomy; lotic ecosystems; Bacillariophyta
