Fool's parsley

Aethusa cynapium has a fusiform root and a smooth hollow branched stem growing to about 80 cm (31 in) high, with much divided (ternately pinnate) smooth leaves with an unpleasant smell, and small compound umbels of small irregular white flowers.

A. cynapium is poisonous when fresh, but safe if dried. A. cynapium's toxic effects are caused at least in part by cynopine, which resembles coniine in its physical and chemical characters as well as physiological actions. The whole plant is toxic with this alkaloid. Toxins like cynopine are destroyed by drying. A. cynapium also contains trideca-7,9,11-trienoic acid, aethusin, aethusanol A, aethusanol B, as well as flavone glycosides such as rutoside, narcissine, and ascorbic acid. The parts of A. cynapium that grow above the ground are sometimes used to make medicine. The plants has been used in traditional medicine to treat complaints in children, infantile cholera, summer diarrhea, convulsions, mental tension, sleep disorders, delirium, and as stomachic. A. cynapium has actually been shown to cause antianxiety effects in mice because it contains trideca-7,9,11-trienoic acid. Poisoning from A. cynapium results in symptoms of heat in the mouth and throat. A post-mortem examination has shown redness of the membrane lining the gullet and windpipe, along with symptoms of slight congestion within the duodenum and stomach. Some toxins are destroyed by drying, and indeed, dried hay containing the plant is not poisonous at all.