We investigated the effects of 1, 5 and 10% of extracts from green and scnesced leaves of P. torta on the germination and growth of lettuce. The higher concentration of extracts affected these processes most. To test whether the inhibition resulted from the acidity of the extracts, lettuce seeds were germinated in the presence of buffered extracts and of an acetic-acid solution with a pH similar to that of the most-concentrated extracts. Adjusting the pH of the extracts did not annul the inhibition of germination and growth of lettuce, and an acetic acid solution with the same pH did not affect these processes. The osmotic effect was evaluated using polyethyleneglycol 6000 solutions, with osmotic potentials similar to the 10% extracts. The ionic effect was determined using leaf ashes solutions with conductivity identical to the 10% extracts., The ash solutions and the polyethyleneglycol did not inhibit the germination or growth of lettuce. Therefore, the inhibitory effects of extracts cannot be attributed to their higher acidity, or to higher concentration of toxic ions, or to the lower osmotic potential. We conclude that allelopathic compounds may be present in the leaves of P. torta, which may explain the spatial pattern of this specie in the Brazilian cerrado.202279285