To obtain floristic and forest structural data from the threatened seasonally dry forests in northwestern Peru, part of the Tumbes-Chocó-Magdalena biodiversity hotspot, we inventoried all plants with dbh ≥ 1 cm in one hectare of forest in the Chaparri Ecological Reserve. We recorded 1255 individuals, representing 24 species, 19 genera and 12 families. The most abundant species was Cordia lutea (Boraginaceae, 249 individuals), the most diverse genus Capparis (Capparaceae) and the most diverse family Leguminosae. These results show that the forest plot in Chaparri represents an impoverished version of the seasonally dry forests in the region and is most similar, compositionally and in structure, to the seasonally dry forests located on the lower western slopes of the northern Peruvian Andes. Exploratory spatial pattern analyses of the most abundant species suggest that their dispersal properties were primarily responsible for the different observed patterns. © International Society for Tropical Ecology.