Hemlock (Conium maculatum L. Umbelliferae) has long been known as a poisonous plant. Toxicity is due to a group of
piperidine alkaloids of which the representative members are
coniine and
gamma-coniceine. The latter is the more toxic and is the first formed biosynthetically. Its levels in relation to
coniine vary widely according to environmental conditions and to provenance of the plants. Surprisingly, these
piperidine alkaloids have turned up in quite unrelated species in the monocotyledons as well as the dicotyledons. Aloes, for instance, important medicinal plants, are not regarded as poisonous although some species are very bitter. Nevertheless a small number of mostly local species contain the
alkaloids, especially
gamma-coniceine and there have been records of human
poisoning. The compounds are recognized by their characteristic mousy smell. Both acute and chronic symptoms have been described. The compounds are
neurotoxins and death results from
respiratory failure, recalling the effects of
curare. Chronic non-lethal ingestion by pregnant livestock leads to foetal malformation. Both acute and chronic toxicity are seen with stock in damp meadows and have been recorded as problems especially in North America. The
alkaloids derive biosynthetically from
acetate units via the
polyketide pathway in contrast to other
piperidine alkaloids which derive from
lysine.