cereus jamacaru dc subsp. jamacaru, has been suffering from severe anthropic pressure, in addition, when their seeds are dispersed, some end up not germinating due to the action of allelochemicals. therefore, the present study was to evaluate the allelopathic effect of the essential oil (eo) from four species over c. jamacaru germination, as well as to identify their constituents. four plants were selected for eo extraction (mesospherum suaveolens (l.) kuntze, lantana montevidensis (spreng.) briq., lantana camara l., and tarenaya spinosa (jacq.) raf.) and the chemical analysis was performed by gc-ms. in order to evaluate the allelopathic activity of the eo’s, the c. jamacaru seeds were treated with the eo’s. the results showed that the eo’s presented heterogeneity in their composition, with m. suaveolens presenting the highest number of constituents (44), followed by l. camara (26), t. spinosa (23) and l. montevidensis (22). all the oils negatively affected the c. jamacaru germination percentage in a concentration-dependent manner. regarding the gvi, the m. suaveolens, l. montevidensis and l. camara oes significantly decreased this index at all analyzed concentrations. based on the results obtained, it is suggested that c. jamacaru should not be sown close to the aforementioned aromatic species in reforestation programs.