The phytosociological structure of a natural park vegetation in the extreme southwestern part of the State of Rio Grande do Sul is studied in an area adjacent to the Quaraí Chico River and under the influence of its riparian forest. The vegetation is characterized by the expressive occurrence of Aspidosperma quebracho Schlecht (quebracho) and Parkinsonia aculeata L. (cina-cina), as well as the presence of numerous species of ciliary forest associated with the three typical species of Inhanduvá Park. Because it is a unique association in Brazil and because it is built in a very fragile ecosystem, it is suggested that it be preserved.
