Research to date on Amazonian swamps has reinforced the impression that tree communities there are dominated by a small, morphologically specialized subset of the regional flora capable of surviving physiologically challenging conditions. In this paper, using data from a large-scale tree inventory in upland, floodplain, and mixed palm swamp forests in Amazonian Ecuador, we report that tree communities growing on well-drained and saturated soils are more similar than previously appreciated. While our data support the traditional view of Amazonian swamp forests as low-diversity tree communities dominated by palms, they also reveal four patterns that have not been well documented in the literature to date: 1) tree communities in these swamp forests are dominated by a phylogenetically diverse oligarchy of 30 frequent and common species; 2) swamp specialists account for < 10% of species and a minority of stems; 3) most tree species recorded in swamps (> 80%) also occur in adjacent well-drained forest types; and 4) many tree species present in swamps are common in well-drained forests (e.g. upland oligarchs account for 34.1% of all swamp stems). These observations imply that, as in the temperate zone, the composition and structure of Amazonian swamp vegetation are determined by a combination of local-scale environmental filters (e.g. plant survival in permanently saturated soils) and landscape-scale patterns and processes (e.g. the composition and structure of tree communities in adjacent non-swamp habitats, the dispersal of propagules from those habitats to swamps). We conclude with suggestions for further research to quantify the relative contributions of these factors in structuring tree communities in Amazonian swamps.