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Abstract
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The coast of Pembrokeshire in Wales is one of the most beautiful parts of the United Kingdom. It is also full of historical sites, including the bay where Henry Tudor landed in order to seize the crown from Richard III of England and establish the Tudor monarchy. My wife and I were walking close to that historic spot during the summer, when a man coming in the opposite direction warned us urgently not to proceed. The path, he explained, was overhung with a plant called water hemlock that was one of the most poisonous indigenous plants in Britain. A mere touch, he said, might cause serious illness to a walker, and ingestion could be fatal. He seemed to know what he was talking about, so we set off in another direction and decided we should probably supplement our interest in coastal walking and history by refreshing our knowledge of botany.
Water hemlock, it appears, is only one of several poisonous hemlock plants. They belong to the same botanical family as many edible vegetables including carrot, celery and parsley, known as Apiaceae or Umbelliferae. The latter term refers to the fact that they flower on clusters of short stalks, spreading out like the ribs of an umbrella. Their grouping as a family is somewhat haphazard, based on their appearance rather than any known common ancestor. Some of the inedible members of the family are merely unpleasant in their effects, like giant hogweed (figure 1), also known as giant cow parsley, which causes a phototoxic rash on contact. A genus called Cicuta includes several fatal species, including Cicuta maculata or water hemlock, the one we almost encountered on our walk (figure 2). Another genus called Conium comprises four species which can be fatal, including poison hemlock, similar in appearance to water hemlock although water hemlock actually has a higher concentration of toxins. Another umbellifer, Oenanthe crocata, the hemlock water dropwort, is equally dangerous. (The hemlock tree, so called because of the apparent similarity of its smell, is a conifer that is unconnected to any of these and harmless)...
Hemlock poisoning is common in horses, sheep, cattle and other livestock, where it can also cause teratogenicity.1 It is less common in humans, although some deaths may be misdiagnosed or go unexplained.2 Where cases are identified, it is often because a family or a group of friends are all suffering the same symptoms after eating a salad or stew containing hemlock.3 Usually, someone has confused these with another innocuous herb or root vegetable. Online guides to wild foraging all explain how to tell the difference between edible, inedible and toxic umbellifers, although the more sensible ones advise people never to identify plants from the internet or books alone but to get expert advice...
Language: en |