The Praia do Sul State Biological Reserve is located on Ilha Grande, State oí Rio de Janeiro, Brazil (23º10' S.; 44º17' W.Gr.). Five plant communities were identified within the limits of this 3600 ha tract: creeping foredune psammophytes, beach ridge forest, coastal plain swamp forest, mangrove and montane forest. The physiognomy of each community is described, including the most common species found and the area of occurrence within the Reserve. A list of approximately 300 species has been compiled to date; the 4 most important families are: Leguminosae, Rubiaceae, Orchidaceae, Bromeliaceae
flora; plant communities; Biological Reserve