Why aethusa is called ‘fool’s parsley?

Known by many different names such as poison parsley, garden hemlock, and dog parsley, Aethusa cynapium is a toxic European weed often mistaken for its parsley look-a-like. Unlike the common herb grown in many gardens, however, this annual plant has dark green foliage with shiny, yellowish-green on its undersides. The plant’s flowers are also white rather than yellow. In addition, fool’s parsley, as it is also called, emits an unpleasant odor when bruised. This aroma is similar to that of the much more powerful and poisonous hemlock.
The plant is also grown in many parts of the United States and Canada, and in spite of its known toxicity, has a past history of use in folk medicine. As a sedative, the herb had been used in the treatment of sleep disorders. Since the plant affects the nervous system, remedies made from the herb were also used to treat convulsions, anxiety, and delirium. In fact, the herbal remedy was thought to relieve a person’s hallucinations of frightening animals. The same remedy was believed to help strengthen concentration as well.
At one time Aethusa cynapium found popularity as a digestive aid. Its use was oftentimes focused on treating young children. For example, fool’s parsley would usually be prescribed for cholera infantum, or the inability to digest milk, as well as for treating bouts of diarrhea. This common remedy also seemed to have more of a positive effect when used in summer or during hot weather. Fool’s parsley was occasionally used for treating vomiting fits as well.
Interestingly, the plant is only deemed poisonous when it’s taken or used fresh. Preparations made from the dried leaves of Aethusa cynapium are not considered harmful, as most of the plant’s toxins are destroyed through the drying process. Most problems occur when this plant is confused with regular parsley, picked fresh, and ingested. Even in small amounts, fool’s parsley can have grave effects.