Poison Hemlock (Conium maculatum) is one of the deadliest plants in North America. This non-native invasive was imported as an ornamental in the late 1800s from Europe, West Asia, and North Africa. The plant contains highly toxic piperidine alkaloid compounds, including coniine and gamma-coniceine, which cause respiratory failure and death in mammals.
The toxins must be ingested or enter through the eyes or nasal passages to induce poisoning; they do not cause skin rashes or blistering. Regardless, this plant should not be handled because sap on the skin can be rubbed into the eyes or accidently ingested while handling food. The roots are more toxic than the leaves and stems; however, all parts of the plant including the seeds should be considered dangerous. Unfortunately, this dangerously toxic plant is becoming more common throughout Ohio including growth in landscape plantings where close proximity to people increases poisoning risks.