Conium maculatum aka Poison Hemlock

Conium maculatum, or poison hemlock, belongs to the carrot family, Apiaceae. Its native range spans Europe, North Africa, and parts of Asia. It reaches Xinjiang, the western Himalaya, and Ethiopia. It is native to Britain and Ireland, too. It has spread in the United States and crowds out native plants. Several states class it as a noxious weed. It grows on roadsides, streambanks, waste ground, and along fences.

This upright herb grows fast and is mainly a biennial. Some plants live longer where sun and moist soil suit them. It reaches 6–10 feet (1.8–3.05 metres) tall. Its spread reaches 4–5 feet (1.2–1.52 metres). In early spring, fine green leaves form a basal rosette. Large leaves divide three or four times into smaller leaflets. They look like parsley and clasp the stems at swollen nodes. The smooth, hollow stems bear purple, red, or brown spots. The pale, fleshy taproot may show red marks. Crushed roots, leaves, and stems give off a bad smell.

Small white flowers form umbels at the stem tips in summer. Each flower has five petals. These clusters give the plant a showy look. The green fruits have wavy ribs and a flattened shape. They turn grey-brown as they ripen. Animals, clothes, and machines carry the seeds to new sites. Seeds can stay in soil for years, which makes control hard. Seeds sown when ripe may sprout in autumn.

Poison hemlock grows in sun or partial shade. It prefers rich, damp soil but tolerates many soil types. In the wild, it avoids acid soil and deep shade. PFAF lists USDA hardiness zones 4–8. Its fine leaves and flower clusters have visual interest. Yet its poison and spread pose serious landscape problems. NC State reports no major insect or disease problems. Handling it can cause a rash in people with sensitive skin.

Every part is poisonous, and eating it can kill. It harms people, dogs, cats, horses, and other grazing animals. Signs include drooling, tremors, weakness, diarrhoea, and paralysis. Its toxins can stop breathing. Seek urgent veterinary care if an animal eats it. PFAF records past food and medicinal uses, but also warns of severe toxicity. Those records do not establish that eating it is safe. Its resemblance to food plants makes mistaken identification a serious risk.