The Anavilhanas islands in Central Amazonia form the world's greatest freshwater archipelago. They are covered with floodplain forests which are periodically inundated by the blackwater of the Rio Negro. Little is known to date about the forest cover, and this study presents a vegetation analysis as a first step towards describing the forest ecosystem of this unique ecosystem. In a plot of 50 × 30 m (0.15 ha), 267 trees were inventoried. Fifty one species belonging to 50 genera of 29 families were determined. The most common family was the Fabaceae, followed by Apocynaceae and Violaceae, both represented by a single species (Tabernaemontana rupicola and Amphirrhox longifolia, respectively). These two species had the highest number of individuals. The canopy structure showed three layers, the densest being at 5-8 m, the second at 14-19 m, and the third at 25-33 m. The vegetation in the study area contains tree species which are characteristic of the 'seasonal igapó', but also of whitewater floodplains and/or non-flooded terra firme. The analysed forest plot represents a mature stage of blackwater floodplain forest with a high number of which have a wide distribution and an ample range of ecological requirements, and a low degree of local endemism.
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