In the present study, we investigate the composition, morphological characteristics and ecological aspects of Euastrum taxa associated with three species of aquatic macrophytes (Utricularia foliosa L., Cabomba caroliniana A. Gray, and Eichhornia azurea Kunth) of the Marimbus do Baiano (Chapada Diamantina), "Caatinga" domain, Bahia State, Brazil. 180 sampling units of periphytic material were analyzed, collected between May/2017-March/2018, revealing a total of 32 taxa. The highest richness was observed in the periphyton of U. foliosa (30), followed by C. caroliniana (24) and E. azurea (23). Nineteen Euastrum taxa were considered rare, whereas five taxa (Euastrum abruptum Nordst., E. abruptum var. chapadae F.M. Costa, G.J.P. Ramos and C.W.N. Moura, E. elegans var. prescottii (Forster) F.M. Costa and C.W.N. Moura, E. evolutum var. integrius West and G.S. West, and E. ornatiscrobiculatum F.M. Costa, I.B. Oliveira and C.W.N. Moura) have stood out for having the highest frequencies of occurrence, being common to the three macrophytes. Most taxa were recorded in an environment with slightly alkaline pH, low electrical conductivity and high dissolved oxygen level. This study highlights the importance of aquatic macrophytes for periphytic communities and expands knowledge about Euastrum in the "Caatinga" domain.