This study focuses on a forested area from southwestern Marajó Island, mouth of Amazon River, aiming to analyse the relationship between plant composition and the latest Quaternary evolution of a land-form with palaeochannel morphologies. A floristic survey aiming to characterize the inner and outer palaeochannel areas indicated similar phytossociological parameters. However, a large volume of species was exclusive to only one of these areas. Although the present-day forest is fairly uniform, a significant variation in floristic composition was recorded according to differences in lithology, topography and hydrology. These were determined by the evolution of the physical environment associated with successive stages of abandonment of a large fluvial drainage system during the latest Pleistocene to Holocene. The results derived from this study indicate that reconstruction of a physical environment is an important parameter to be taken into account before establishing models aiming to explain the distribution of modern plant species in tropical areas.