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A detailed phytosociological analysis of seasonally inundated grasslands with Echinochloa colona in semi-arid and sub-humid tropical West Africa is presented. Such grasslands are flooded during the rainy season and dry up during the rest of the year. E. colona is a thermo-cosmopolitan, annual and hydrophilous grass species. In West Africa, it is widely distributed and highly appreciated as a fodder plant for livestock. Our study area comprised subareas in Burkina Faso, Niger and Mall, covering two bioclimatic zones. The floristic structure of the vegetation was documented with 114 releves, which were classified manually, and with a cluster analysis. Additionally, they were ordinated to characterize main floristic gradients. We describe a new alliance, the Panico laeti-Echinochloion colonae. It consists of five new associations (Panicetum laeti, Eragrostietum pilosae, Dicliptero verticillatae-Echinochloetum colonae, Tephrosio pedicellatae-Echinochloetum colonae, and Crinetum zeylanici). These plant communities show high cover values and colonize sandy, sandy-loamy or loamy to clayey soils that can be water-saturated or repeatedly inundated only during the rainy season. Soil type and topographical situation with duration of flooding were the most important differentiating factors, whereas precipitation was a secondary one. The predominant life-form was annual grasses. The results of the manual classification are largely congruent with the results of the multivariate techniques. In some cases, the floristic turnover between the plant communities has a continuum character. In particular, stands of Panicetum laeti are often intermixed with other associations. Four communities are documented for Burkina Faso, two for Niger and only one for Mali. Larger distribution areas of the newly described syntaxa beyond the study area can be assumed. Echinochloa colona is documented in other plant communities in various regions of tropical West and Central Africa, and colonizes not only inundated grasslands but also water meadows.