Senecio inaequidens D.C., an Asteraceae from Sout-Africa, is a successful invasive species in Europe. In the South of France it is a real problem in pastures where the plant may grow abundantly, while it is toxic for the cattle. This pluriannual species spreads rapidly through its numerous seeds and is able to colonize any distributed area. As alkaloids produced by Senecio are known to accumulate in roots (Hartmann, 1994), their potential effect was tested in order to evaluate if allelopathy is a component of Senecio ability to invade those areas [Authors' introduction].