The dispersal units of the Compositae found during the purity tests and the weed tests, carried out in the Seed Analisys Laboratories, must be correctly identified. The main objective of this work was too illustrate and to characterize anatomo-morphologically the achenes of the weed species of Centaurea cyanus, Centaurea jacea L., Centaurea repens L., Cirsium arvense (L.), Scop., Cirsium vulgare (Savi.) Ten., Ateratum conyzoides L., Rudbeckia hirta L., Ambrosia artemissifolia L., Ambrosia polystachya DC., Galinsoga ciliata (Raf.) Blake, Galinsoga parviflora Cav., Emilia sonchifolia DC e Erechtites hieracifolia (L.) Rafin., to allow a more sure and clear taxonomical identification at the level of species, as well as to characterize morphologically theirs seedlings. A taxonomical key in order to help the identification of thedipersal units and a discription of the achenes and the seedlings of each studied specie, were carried out.