The Fool's Parsley (Aethusa cynapium) or Fool's Cicely or Poison Parsley is an annual (rarely biennial) herb in the plant family Apiaceae, native to Europe, western Asia and northwest Africa. It is the only member of the genus Aethusa.
It has a fusiform root and a smooth hollow branched stem growing to about 80 cm high, with much divided (ternately pinnate) smooth leaves with an unpleasant smell, and small compound umbels of small irregular white flowers. It is related to Hemlock and Water-dropwort and like them is poisonous, though less so than Hemlock. Poisoning from Fool's Parsley showed symptoms of heat in the mouth and throat and a post-mortem examination showed redness of the lining membrane of the gullet and windpipe and slight congestion of the duodenum and stomach. Since some toxins are destroyed by drying, hay containing the plant is not poisonous. Symptoms of poisoning are heat in the mouth and throat.
It has been introduced into many other parts of the world and is a common weed in cultivated ground.