When alien plants become health hazards: An applied study on toxic and allergenic risks in Italy

Societal Impact Statement Alien plants are often studied for their ecological harm, but their risks to human and animal health remain poorly documented. This study provides the first comprehensive catalogue of poisonous and allergenic alien plants in Italy, identifying which species are dangerous, where they grow and who is most at risk—from children in city parks to pets and livestock. By also revealing their unexpected benefits, such as medicinal uses and support for wildlife, the findings offer a balanced foundation for public awareness campaigns, targeted management near schools and hospitals and informed policy on living safely with alien flora. Summary Traditional knowledge of plant safety is declining, while alien species keep spreading across Italy. Some of these plants produce toxins or allergens, yet no comprehensive inventory existed for the country. This study therefore compiled the first complete catalogue of poisonous and allergenic alien plants in Italy, covering risks to humans, pets and livestock while also assessing their potential benefits. The authors reviewed published floras, regional checklists, toxicology reports and ethnobotanical literature. For each taxon they recorded origin, introduction pathway, habitat, distribution, toxic compounds, clinical effects and beneficial uses (medicinal, wildlife food, beekeeping). Hazard levels were assigned based on clinical severity. A total of 205 alien taxa were identified. Most are toxic (158 taxa), 47 are allergenic, and 23 can be lethal. Urban environments host the highest number of hazardous species. However, 152 taxa have medicinal properties, 63 are of beekeeping interest, and 38 support wildlife. Five particularly dangerous species combine high lethality, invasiveness and wide distribution. Alien poisonous plants are a genuine health risk, but blanket eradication is often unrealistic and unwise because many also provide ecological and medicinal benefits. Targeted management, public awareness campaigns and risk monitoring near schools and hospitals are more effective strategies than indiscriminate removal.