Precise identífication of weed seeds is required in a seed analysis laboratory, as well as in several other areas of seed technology. The main objective of this work was the characterization of the morphological features of the seeds, that permit the taxonomical identification of species and genus. Description and photograhs of plants and seeds were carried out in the following species: Acanthospermum australe (Loef.) O. Kuntz; Xanthium cavanillesii Schoww.; Quamoclit coccinea Moench; Cenchrus echinatus L.; Portulaca oleracea L.; Richardia brasiliensis Gomes; Datura stramonium L. and Solanum sisymbriifolium Lam. The identification of the plant material was based on their morphological characteristics such as shape, structure and size of roots, shoots, leaves, inflorescence, flowers, fruits and seeds. Regarding the seeds, the followings descriptive characteristics were considered: shape, cross section, size, surface features (external appearence, color, texture of the seed coats, apendages of the seed coat, etc.), hilum (color, shape, position and tiltress), the micropile, the raffia, the presence or absence of associated parts (such as arils, funiculus and caruncles), the number of layers of the seed coat, storage tissues - endosperm (color, quantity and quality), embryo (absolute and relative sizes, color, type, shape of the cotyledons, etc).