Abstract
The taxonomic study about the genus Nitzschia Hassall, the Lagoon Casamento and Butiazal de Tapes areas, located at 30º40'-30º10'S e 50º30'-51º30'W, was based in plankton and metaphyton samples, collected in 21 stations including different environments (interconnected lakes, isolated lakes, swamps and ponds), in the fall and spring of 2003. The results revealed the presence of 35 taxa specific and infra-specific, highlighting 11 new records for the State and 5 new ones for the Coastal Plains of Rio Grande do Sul. Regarding the habit and 91% occurred in plankton and metaphyton, only 9% were restricted to metaphyton. The Lagoon do Casamento area presented greater richness (35 taxa) compared to the Butiazal de Tapes area (13 taxa), probably due to the presence of environments in connection with the Patos lagoon, that has a rich flora of Nitzschia , associated to a high conductivity and water pH conditions. Descriptions, illustrations and comments about the morphological and/or metric variations and of the taxa are presented.
Key words:
diatoms; morphology; taxonomy