Elionurus muticus is a native grass from Brazil that has been shown to have large variability in the chemical constituents of its essential oil. However, few studies have evaluated this species. The aims of this study were to chemically characterize four wild populations of E. muticus that were collected in southern Brazil as well as to evaluate the allelopathic effect of the essential oil, which is rich in citral. Chemical analyses were performed using gas chromatography and mass spectrometry. The phytotoxic activity was evaluated with onion and lettuce seeds. The results showed that the studied populations have chemical variability based on their geographic origin, which indicates the possibility of chemotypes. The results obtained with E. muticus essential oil, reveals phytotoxic activity on the germination and growth of lettuce and onion.