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Prunus laurocerasus, cherry laurel
A vigorous shrub often used to provide screening but care needs to be taken when handling prunings.
Meaning of the Name
‘Lauro’, ‘laurel’ and ‘cerasus’, ‘cherry’ and, hence, cherry laurel
Common Names and Synonyms
cherry laurel, laurel, English laurel
How Poisonous, How Harmful?
Prunus laurocerasus, cherry laurel
The leaves and fruit pips contain cyanolipids that are capable of releasing cyanide and benzaldehyde. The latter has the characteristic almond smell associated with cyanide.
1.5% cyanogenic glycosides are present in the leaves. During maceration, i.e. chewing, this becomes glucose, hydrogen cyanide (prussic acid), and benzaldehyde. Cyanide starves the central nervous system of oxygen and, thus, causes death.
The Prunus laurocerasus has enough of the poison in the leaves to be used by entymologists as a way of killing insect specimens without physical damage. They seal the live insects in a vessel containing the crushed leaves.
Confusing the two laurels and using the leaves of this plant as bay in cooking has resulted in poisoning. If this occurs prompt treatment is essential.
In September 2015, I was contacted by someone who had been picking blackberries with her grandchildren. She made ice lollies with some of the fruit. When her grandchildren tried one they said they didn't like the taste so didn't do more than have a few licks. That night, one of them was sick but not seriously so no-one thought anything of it. When grandmother ate a whole lolly, however, she suffered violent vomiting within an hour.
When she checked a bag of frozen fruit, she saw a few plain berries in amongst the blackberries. The bramble bushes they picked from were growing under and through a cherry laurel and she realised they had picked some laurel berries in error.
The number of such incidents is very small but it is a reminder of the need to identify what you are picking and it is probably wise not to pick in any area where there could be confusion between a tasty fruit and a toxic berry.
Other than this incident, in modern times most incidents noted with this plant are related to the smell emanating from chipped prunings. The following are typical examples.
Using the contact form on this site, a correspondent told me about the time he filled his car with bagged shreddings from his large cherry laurel and set off for the tip. On the way, he could smell almonds and thought 'Hmmm, cake!' before realising what he was smelling. He opened all the car windows and suffered no ill effects (other than the disappointment of not having any cake).
A woman employed a contract gardener to remove a tree. He used a chipper to deal with the smaller branches. She asked him to also prune a run of cherry laurel and he said he would but he wouldn’t chip it having, on a previous occasion, almost passed out from the cyanide fumes coming off the chipper.
A tree surgeon talked about smelling almonds when he opened a van full of laurel shreddings.
But, the story of someone passing out while driving a van full of laurel prunings seems to be apocryphal. I have spoken to people who noted the smell associated with cyanide when using a chipper but, since this is an activity performed in the open air, the chances of becoming unwell seem small.
But, until the middle to late 19th century, cherry-laurel water, made by distillation of the leaves, was a common source of hydrocyanic acid, also known as prussic acid. In his 'Treatise on Poisons', published in the 1840s, Sir Robert Christison, writing about the various plant sources of hydrocyanic acid says 'they have been repeatedly taken by accident ; they have often been resorted to for committing suicide ; and they have likewise been employed as the instruments of murder.'
Christison illustrates his point about accidental consumption with the story of a chemist's servant who drank a large glass of hydrocyanic acid, thinking it was a liqueur, after her master had left it out by mistake. She died within two minutes.
Prunus laurocerasus, cherry laurel
Perhaps the best known case of murder by cherry-laurel water was that of John Donellan who murdered his brother-in-law, Sir Theodosius Boughton, on 30th August 1780. At his trial on 30th March 1781, most of the evidence against Donellan was circumstantial; he stood to benefit financially from Boughton's death before the age of 21, he had spent some time expressing the opinion that Boughton was of a weak constitution and would not last long, he had persuaded Boughton to leave his prescribed medication out, where Donellan could access it, to avoid Boughton forgetting to take it, he had distillation equipment in his room supposedly for producing rose water, he poured away the rest of the bottle of medicine as soon as Boughton died and washed it out thoroughly and he attempted to frustrate his own father's efforts to have the cadaver examined.
But, the evidence which almost certainly convicted him was the bitter almond smell always associated with cyanide. Lady Boughton, Sir Thoedosius' mother had given him the fatal draught and commented on the bitter almond smell at the time. In court, when asked to smell a liquid, without knowing what it was, she identified the same smell as being cherry-laurel water. One of the doctors, Dr Rattray, who did, eventually, examine the badly decayed remains also commented on the strong smell of bitter almonds on opening the stomach. Bizarrely, this evidence was elicited by cross examination by the defence lawyer who was hoping to show that the body had decomposed too much to provide any reliable information.
The case provides an interesting example of the notion that getting away with murder is easiest if no-one suspects murder to have occurred. As soon as someone notices something odd, as Lady Boughton did, the chance of a death going uninvestigated diminishes.
In his defence, Donellan sought to establish that Sir Theodosius had contracted syphilis as a result of consorting with prostitutes throughout his time at boarding school and that the disease and the mercury treatment he was receiving were the cause of death. It was also said that Mr Powell, an apothecary who seems to have functioned as the family doctor, prescribed Goulard's Extract, a mixture of lead acetate and lead oxide.
Donellan's army career had ended after a bribery scandal so his questionable character coupled with the financial motive for ensuring that Sir Theodosius died before reaching 21 made a guilty verdict easy to reach and he was hanged on 2nd April, just four days after his trial began.
In August 2010, this case featured in an episode of the BBC TV programme 'Who Do You Think You Are?' featuring Alexander Armstrong who is a direct descendant of the brother of the man who inherited Sir Theodosius' title, that ancestor, in turn, inheriting the title from his brother.
Folklore and Facts
A post on the UK Tree Care Mailing List suggests that care should be taken when chipping the plant because this could cause similar maceration to chewing.
Graham Young, the St Albans’ Poisoner mostly used antimony and thallium but, when in Broadmoor for a time, used laurel leaves to kill at least one person. His confession was ignored because, apparently, any death in Broadmoor produces a great number of ‘confessions’.
Other members of the Prunus genus, especially apricot and bitter almonds have been the cause of poisonings both in cattle and humans.