Contribution to the flora of the Kostroma region based on the materials of 2021-2022

The paper presents new data on vascular flora of Kostroma Oblast (European Russia) obtained during field studies in 2021-2022. Two native species (Galium rivale (Sm.) Griseb., Sanicula europaea L.) and two alien ones (Bromus riparius Rehmann, Veronica agrestis L.) are new to the Kostroma Oblast. For eleven more species, we report new localities in the region, as the data on their current distribution are scarce. From these species, nine are natives rare in the region (i.e. Agrostis vinealis Schreb., Aristolochia clematitis L., Avenula pubescens (Huds.) Dumort., Carex arnellii Christ ex Scheutz, Epilobium roseum (Schreb.) Schreb., Equisetum scirpoides Michx., Festuca altissima All., Geranium palustre L., and Polygonatum multiflorum (L.) All.), one species is expansive native (Salvinia natans (L.) All.), and one species is naturalized neophyte (Coronilla varia L.). For each species, a list of recorded localities and their habitat preferences are given. Data presented are important for the evaluation of the alien species spread and for the nature conservation in the region.