The study of seed morphology is not well developed in Brazil. Nevertheless, this characteristic remains remarkably constant under varying environmental conditions and may be used as suitable criteria for the taxonomical identification of species, as well as the whole plants do. The main objective of this work was to make an illustrative description and characterize morphologically the weed dispersal units of Anagallis arvensis L., Cardiospermum halicacabum L., Apium leptophyllum (Pers.) F. Muell., Euphorbia hirta L. and Euphorbia serpens H.B.K., to permit a clear taxonomical diferenciation between them, as well as, prepare a brief description of the fruits and plants of these species. Two different taxonomical keys are presented in order to help in the identification of the dispersal units and of the plants. For each species, a detailed characterization of the dispersal units was carried out utilizing external and internal morphology. A morphological charactenzation of the studied genus, is also presented. The scientific and common names were included and, whenever possible, a description of the habitat, life cycle, phenology, type of reproduction, geographical distribution and other informations, such as the crop in which it is considered as a weed, and the agricultural seeds in which the dispersal unit was found as a weed seed.