poisons part 2

6th March 2013

Yesterday we looked at some plant poisons which are responsible for most serious poisonings in the UK.  However there are many other plant toxins which although perhaps not deadly unless consumed in large quantities can still cause ill effects if ingested.


These are bitter and astringent compounds found in many plants which because of their unpleasant taste are present to deter herbivores from consuming the plant. Although not toxic in small quantities some are converted in the gut to pyrogallol which is toxic or in large quantities they can deter the digestion of protein and cause stomach aches.  They also bind to protein and may be carcinogenic if consumed in quantity over a long time.  Acorns and Sloes are particularly high in tannins.

Sloes – full of tannins



These are light sensitive compounds which if secreted onto the skin react in sunlight to cause skin reactions and blistering. The most well known plant that contains these chemicals is Giant Hogweed but other members of the family like the closely related Hogweed and sometimes even Cow Parsley although they contain smaller amounts can still cause sensitivity.

Hemlock – the sap can cause skin irrations in sunlight



Although not in a particular  chemical family, there are some plant compounds that are well known for causing allergic responses in people. One well known allergen is primin a chemical found in Primroses and Leylandii Cypress can often cause an allergic reaction in people.



Occasionally plants produce a protein that may have toxic properties.  Mistletoe contains toxic proteins including viscotoxin and viscumin. The most toxic naturally occurring compound is a protein called ricin found in the Castor Oil Plant.

Other plants contain enzymes which are proteins. Bracken and Horsetails contain an enzyme called thiaminase which breaks down vitamin B1 and can cause a deficiency.


And the rest

Other compounds found in plants that can be toxic includes phenols- found in cypresses etc., esters – found in Petty Spurge, methylamine found in Dog’s Mercury to name just a few.

Dog’s Mecury – contains saponins and methylamine


In addition some plants contain irritant chemicals. Nettles contain a veritable cocktail of chemicals in their sting which causes the irritation; formic acid , serotonin, histamine and acetylcholine.

This list of harmful plant chemicals is much longer than those listed here, and the toxic compounds found in fungi are often completely different again.  There are still many plant and fungi species where the exact toxin and its method of action is unknown. It all goes to highlight that the forager should never under estimate the costs of making a mistake.


Kev Palmer

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