In this study, the structure of the vegetation and the species diversity of three remnants of riparian forest of the right bank of the upper Paraná river (22º43'-45'S; 53º15'-18'W) were analysed and compared. In each forest remnant, 3,150m² were marked and subdivided into 21 continuous plots of 150m² each. Only trees with a perimeter at breast height > 15cm were measured. Fifity eigth species belonging to 46 genera and 30 families were found. Two taxa at the family level were still unidentified. The families Myrtaceae and Lauraceae had the highest number of species (five each), followed by Mimosaceae (four), Annonaceae and Rubiaceae (three each). The richest genera in terms of number of species were Nectandra, four, and Eugenia, Inga, Pouteria, Psidium and Sloanea, with two each. The specific diversity index for the downstream, the intermediate, and the upstream site were respectively 2.94, 2.52 and 2.88. The Sorensen similarity index was high between sites, ranging from 54% to 65%. Only 16 (26.7%) of the total of the species occurred in the three sites, the remaining species occurring in either one or two sites. Out of the 10 species with the highest importance value, only Cecropiapachystachya and Inga uruguensis were common in the three sites. The phytosociological analysis demonstrated that the intermediate remnant is in a less mature successional stage. The homogeneity of topography and soil indicated that the structural differences between the remnants might be related to anthropic action.
floristic; phytosociology; riparian forest; alluvial forest; Paraná river; floodplain