Impatiens capensisis an annual plant native to eastern North America that is currentlyspreading across Europe. In Poland, due to this plant’s rapid spread in the secondaryrange and high competitiveness in relation to native species, it is considered a locallyinvasive species. The microstructure of seeds is an important tool for solving varioustaxonomic problems and also provides data useful for determining the impact of variousenvironmental factors on the phenotypic variability of species. This issue is particularlyimportant in regard to invasive species which occupy a wide range of habitats in theinvaded range. There are few reports on seed size and thus far no descriptions of theseed ultrastructure ofI. capensisin the analyzed literature. We present new data onthe seed morphology ofI. capensisgrowing in different habitats and conditions inthe secondary range of the species. The studied populations differed significantly ineach of the investigated traits (seed length, width, circumference, area, roundness,and mass). Our findings showed that anthropogenic disturbances in habitats andsome soil parameters (presence of carbonates, potassium, loose sand, and moisture)were statistically significant with various seed sizes and morphology in the studiedpopulations ofI. capensis. Moreover, our studies showed maximum seed length (5.74mm) and width (3.21 mm) exceeding those values given in the available literature. Forthe first time, we also provide a detailed SEM study of the ultrastructure of the seedcoat ofI. capensis. There are two types of epidermal cells on the seeds: (a) between theribs (elongated with straight anticlinal walls, slightly concave outer periclinal walls, andmicropapillate secondary sculpture on the edges with anticyclic walls), and (b) on theribs (isodiametric cells with straight anticlinal walls and concave outer periclinal walls). Unlike the variability of size and weight of seeds, the coat ornamentation has turnedout to be a steady feature within the studied secondary range ofI. capensis.