Premise of research. This represents one of the first studies of the ecology, diversity, and structure of campos de murundus termite savannas in the vast seasonal wetlands of southern Amazonia. We aimed to improve understanding of this threatened system by assessing species richness, abundance, and co-occurrence among trees and herbs of murundus (earth mounds), investigating the environmental and biological mechanisms underlying these patterns, and discussing implications for biodiversity conservation. Methodology. We identified every tree, shrub, subshrub, and herb on 373 murundus across 11 ha at Araguaia State Park, southern Amazonia. We constructed species abundance distributions of trees and herbs, assessed best-fit models, and tested for nonrandom patterns of species co-occurrence using checkerboard scores. Using detrended correspondence analysis (DCA), we assessed the affinities among tree species and their positions in murundus. Pivotal results. A total of 166 species, 123 genera, and 49 families occupied the murundus. The species abundance distribution of trees followed a lognormal distribution, whereas that of herbs was best described by a Mandelbrot distribution. Observed C-score indices for trees and herbs were significantly larger than expected by chance, indicating nonrandom distributions and species segregation among murundus. DCA revealed a strong gradient in species occurrence within murundus, suggesting that internal structuring may be hydrologically based (e.g., variation in mound microrelief). Conclusions. Environmental (e.g., flooding) and biological (e.g., competition between plants) factors are important for controlling the occurrence of tree and herb species on the murundus. The murundus function as critical bases for the maintenance of species diversity in this extensive floodplain, thereby deserving recognition among ecosystems with high conservation priorities.