This paper presents the results of research on ephemerophytes of the alien portion of the flora of the Romensko-Poltavsky Geobotanical District (north-eastern Ukraine). It is a detailed study of this group of plants, conducted for the first time in the Ukraine. The checklist of alien vascular plants contains 345 species, of which 27 species are ephemerophytes (or 8%): Adonis aestivalis, A. annua, Papaver albiflorum, Urtica cannabina, Gypsophila perfoliata, Atriplex micrantha, Chenopodium × preissmannii, Ch. × thellungii, Rumex longifolius, Sisymbrium polymorphum, Euphorbia humifusa, Malus sylvestris, Onobrychis viciifolia, Astrodaucus orientalis, Datura tatula, Solanum schultesii, Lindernia procumbens, Melampyrum cristatum, Helianthus annuus, Petasites spurius, Xanthium ripicola × Xanthium albinum, Echinochloa tzvelevii, Panicum capillare, Panicum capillare L. subsp. barvipulvinatum, Phalaris canariensis, Setaria ×ambigua, Sorghum halepense. The basis of this work is original data of the author obtained during field studies, and a critical study of the literature, archival, cartographic materials and herbarium collections, and the use of classical methods of botanical classification. Complex research of this group of plants was conducted and as a result of these investigations the following characteristics were established: a predominance of kenophytes of Mediterranean origin in this group, species of arid areas, cosmopolitan species with a diffuse type of space structure, therophytes, herbaceous monocarpic plants, mesotrophes, heliophytes and xeromesophytes, with an insignificant degree of impact on native plant communities and with a limited distribution within the study region. The combination of these results indicates that ephemerophytes comprise a temporary, unstable component of the flora of this region of the Ukraine. The paper provides maps of the distribution of these 27 species.
