Perboni, L.T. creator Agostinetto, D. creator Gazola, J. creator Tessaro, D. creator Teixeira, M.M. creator Neutzling, A. creator text periodical abstract or summary bl. continuing eng ABSTRACT Background: Plants synthesize compounds of specialized metabolism to defend themselves against biotic and abiotic stresses. These compounds could be used as models for pesticide development. Among the species that have not yet been studied for the potential to produce active compounds is the kidney leaf mud plantain (Heteranthera reniformis). Objective: The goal was to evaluate the effect of hexanic, ethyl acetate and methanolic extracts of H. reniformis leaves on cress (Lepidium sativum) seed germination to determine which one have the highest biological activity; and to evaluate different concentrations of extract with the highest biological activity on lettuce (Lactuca sativa), barnyard grass (Echinochloa sp.) and giant arrowhead (Sagittaria montevidensis) germination. Methods: The seeds were placed on petri dishes containing two sheets of germitest paper, and after the application of the extract, they were sealed and placed in growth chambers with controlled temperature and photoperiod. The variables analyzed were 1st and 2nd germination count, germination speed index and length of the aerial part and roots. Results: The ethyl acetate extract provided greater phytotoxicity on cress than the other extracts. In general, the highest concentration of ethyl acetate extract was the most efficient in reducing variables for all species. Conclusions: The ethyl acetate extract of H. reniformis presents inhibitory activity on the seeds of cress, lettuce, giant arrowhead and barnyard grass, but this activity was dependent on the concentration of the extract and the species studied. H. reniformis synthesizes compounds with phytotoxic activity and purification of extracts is required to isolate, identify and characterize the action mechanism of the compounds with herbicide activity, so that in the future these can be used as models for the development of herbicides. Keywords: Heteranthera reniformis extracts weeds suppression Publicação on-line; 24 ref.; 10 tables; 4 illus.; Summary (En) PLANTA AQUÁTICA EXTRATO ERVA DANINHA Londrina-PR : Sociedade Brasileira da Ciência das Plantas Daninhas, 1978 2023-031024 0100-8358; 1806-9681 (on-line) BR2023000834 v. 38 p. 1-10; (2020) https://www.scielo.br/j/pd/a/BKd9kDdY46SHtqmSPgL3zbc/?format=pdf&lang=en https://www.scielo.br/j/pd/a/BKd9kDdY46SHtqmSPgL3zbc/?format=pdf&lang=en BR-BrBNA 230807 20230922110933.0 eng