Abstract
This study on the Desmodesmus An, Friedl & Hegew. and Scenedesmus Meyen flora was developed in isolated ponds, interlinked ponds, marshes, dams and lotic environments of the Rio Grande do Sul Coastal Plain. 41 samples collected in autumn and spring 2003 were analysed. 13 species and three varieties of Desmodesmus and two species and one variety of Scenedesmus were identified. Four new combinations were proposed: Desmodesmus granulatus (W. & G.S. West.) Hentschke & Torgan, D. heteracanthus (Guerr.) Hentschke & Torgan, D. microspina (Chod.) Hentschke & Torgan and D. spinoso- aculeolatus (Chod.) Hentschke & Torgan. The highest values of richness and density were observed in samples with lower pH. The average density (ind.mL-1) of Desmodesmus and Scenedesmus in spring was significantly higher than in autumn, probably due to higher water temperature and decreased water level, enabling a higher concentration of organisms.
Key words:
Chlorophyta; density; water pulse; richness; taxonomy