Achyrocline satureioides (Lam.) DC [Marcela] a native plant from Brazil, it is exploited through the cull and gathering practice due to its high medicinal value. In its habitat, it grows in clusters that suggests the existence of amensalism. This characteristic can influence the cultivation and harvesting of this species for economic reasons, and it can also influence the way the area is managed. Based on these field observations, the hypothesis that there exist an allelopathic activity in A. satureioides was formulated. In order to test this hypothesis bioassays of germination and initial growth were carried out. In these experiments, the test plant used was Lactuca sativa L. var. Regina. From flowers and aerial parts of Marcela, aqueous extracts with a concentration of 5, 2,5, and 1% were obtained. In each extract the pH, osmotic potential and yield was evaluated. The germination after 24 hours was defined as a radicule length igual or higher than 1 mm. The growth was evaluated through the measurement of the radicule's and hypocotyl's length on the sixth day after germination. The results showed that different concentrations of aqueous extracts inhibited the germination and stimulated the growth of the lettuce cultivar. The extracts taken from the young aerial parts when more concentrated showed higher germination inhibition and also higher growth stimulation. These data indicate that A. satureioides (Lam.) DC. presents an allelopathic activity because its extracts interfere with germination and growth without any interference of pH or osmotic potential.
