Seed identification is of major importance in seed testing. Much weed plants cause great damages in economical crops, when the seed production was considered. The morphological characteristics of the dispersal units remain remarkably constant under varying environmental conditions and they may be used as suitable criteria for the taxonomical identification of the species, as well as the whole plants do. The objective of this work was the ilustration and the description of the external and internal characteristics of the dispersal units, such as shape, type, size and position of the embryo in relation to the storage tissue (endosperm), in order to allow a correct identification of the weed species of Thunbergia alata Bojer (Acanthaceae), Flaveria bidentis (L.) O.Ktze. e Wedelia paludosa DC. (Asteraceae), Neslia panicularta Desv. (Brassicaceae) e Alcalypha arvensis Poepp. & Endl (Euphorbiaceae), as well as the common names.