In the summer of 2025, a population of Toxicodendron radicans (L.) Kuntze, commonly known as eastern poison ivy, was discovered growing behind the Kaunas Botanical Garden in Lithuania. The discovered population of Toxicodendron radicans was observed occupying two contrasting habitat types: grassland and a nearby woodland. A negative relationship was found between Toxicodendron radicans coverage and plant species richness in both habitats (rs = –0.62; p < 0.05). The coverage of Toxicodendron radicans and other plant species in the grassland showed a strong negative relationship (rs = –0.95; p < 0.001). In contrast, this relationship was weak and not significant in woodland habitat (rs = –0.22; p = 0.34). This finding represents the first verified record of the species in the country and constitutes the northernmost documented record of its casual presence in Europe. It also underscores important concerns regarding the role of botanical gardens as potential hubs for the introduction and establishment of alien plant species. The detection of Toxicodendron radicans in Kaunas underscores the need for rigorous monitoring, risk assessment, and management measures within and around botanical gardens to prevent the unintentional spread of potentially harmful or allergenic species into surrounding ecosystems.