ABSTRACT Ecological communities are compared by the similarity or distinctness of their species. Taking into account community composition at a determined site, one could expect a similar reasoning to explain differences in both taxonomic and functional composition due to environmental gradients. We aim to evaluate spatial variation in functional composition of aquatic macrophyte assemblages in a Neotropical floodplain. The studied floodplain is characterized by encompassing different ecoregions considering both differences in environmental features and macrophyte taxonomic composition. Therefore, we hypothesized that macrophyte functional composition would differ among ecoregions but instead found limited differences in functional composition. There was only a little evidence that some life forms are more or less observed in certain ecoregions. Thus, the considerable environmental heterogeneity found at the ecoregion scale is reflected only in taxonomic, and not in functional composition. This result can be explained by different species having high functional redundancy: different functional traits could be recorded in all ecoregions. Therefore, we suggest that the functioning of the entire ecosystem is probably insured by species functional redundancy in this Neotropical floodplain. Nonetheless, we cannot rule out the fact that trait choice could affect interpretations, and so trait selection should be better explored, particularly for aquatic macrophytes.