Among the several factors that negatively influence cowpea culture, weeds have been responsible for the reduction of growth, development and productive performance of the crop, making it necessary to establish management strategies based on phytosociological studies of weed species in growing areas. Therefore, the objective of this research was to evaluate the floristic composition of weeds, aiming to identify the main species and their dynamics, and to consider their distribution in time and space as pertaining to the cultivation of a modern variety of cowpea, cv. BRS Novaera, in dystrophic Red-Yellow Argisol, in the Midnorth region of the state of Piaui, Brazil. The phytosociological survey of weeds was carried out in three sessions: the first one was immediately before the area was desiccated with glyphosate (15 days before sowing the cowpea), and the others were at 20 and 40 days after sowing (DAS). Following the quantification of species and number of individuals, the following phytosociological parameters were calculated: frequency and relative frequency; density and relative density; abundance and relative abundance; and importance value index. It was concluded that there were few changes in the floristic composition of the weed community according to the epoch of the phytosociological surveys. The main weed plants at 20 DAS of cowpea (vegetative phase) were 'Chamaesyce hirta, Digitaria insularis, Alternanthera tenella, Cleome affinis, Mollugo verticillata' and 'Portulaca oleracea'. At 40 days (reproductive phase), the weed species with a large establishment and acting as potential competitors with cv. BRS Novaera cowpea were 'Digitaria insularis, Chamaesyce hirta' and 'Mollugo verticillata'.