In Scotland, this plant is most often found in urban environments, associated with pavements, old buildings and walls. It is also well-known as a weed of arable crops. As its English name suggests, it resembles Parsley (but only fools would make the mistake of using a poisonous plant as a culinary herb).
Aethusa cynapium by Otto Wilhelm Thomé (1840–1925) the German botanist/artist from Cologne.
Like Parsley, it is hairless and appears in early summer with fresh green, much-divided, leaves. Its leaves are more divided than those of parsley, they smell foul (‘mousey’) when crushed, and Fool’s Parsley has unmistakeable long and pointed bracteoles that hang on the outer side of the umbels (see the images below). Also its stems are usually hollow, not solid like Parsley. And Parsley (Petroselinum crispum) rarely grows wild in this country, and so confusion of the species and subsequent poisoning is almost unknown.
Aethusa cynapium. Note the general similarity to many members of the Apiaceae, but Fool’s Parsley has the long green bracteoles on the outer side of the umbels. This specimen has bracteoles that are much longer than the individual flower stalks, a defining feature of the commonest subspecies Aethusa cynapium ssp. cynapium. Images: Chris Jeffree.
It belongs to the Apiaceae, the family of carrot, celery, coriander and parsley. Unlike most members, this one is an annual plant, germinating in the autumn or late spring. There are two well-defined subspecies, a tall version (up to 1 metre) called cynapium and a short one (20 cm), agrestis. Edward Salisbury in his old but still-useful book Weeds and Aliens calls them ‘strains’, and considers the short one to have evolved through avoidance of the scythe and/or the combine-harvester.
Is it a native plant? Clapham’s 1987 Flora of the British Isles said it is; however, in the New Flora, Stace says ssp. cynapium is native but ssp. agrestis is an archaeophyte-colonist. Archaeophytes are introduced (alien) plants that have been with us for a long time (arriving before 1500), whilst ‘colonists’ are associated with habitats controlled by human activities. This species was first recorded in Britain in 1597, but it was probably present as a native during neolithic times (for example, there is mention of it at an archaeological site at Stonehenge, but the authors do not seem to be sure of the identification of charred remains). If you like archaeology, have a look at their report.
Flowers and fruits. Images: Chris Jeffree
Most recorders do not distinguish between the two subspecies and so it is hard to comment on their relative distributions. However, Stace’s 2019 New Flora says ssp. cynapium is found on “cultivated and waste ground throughout the British Isles” with the exception of much of Central and Northern Scotland whereas ssp. agrestis is more southern.
All parts of the plant are said to be poisonous, but much less poisonous than the related species Conium maculatum (Hemlock) and Oenanthe crocata (Hemlock Water Dropwort). For clinical symptoms of poisoning, the Handbook by Nelson et al (2007) has this to say:
“Clinical Findings: Ingestion can cause nausea, vomiting, diaphoresis, and headache. Toxicity resembles poisoning from cicutoxin. However, the concentration of toxin is insufficient to cause serious effects in most cases. If poisoning occurs, onset of effect is rapid, usually within 1 hour of ingestion. Symptoms include nausea, vomiting, salivation, and lockjaw. Generalized seizures also may occur. Death may occur if seizures do not terminate”.
However, there is a contradictory report from The European Food Safety Authority (EFSA) saying this:
“…poisonous potential is questionable as no toxicity is found in mice and guinea pigs. Probably toxic information comes from confusion with Conium poisoning or plants infected with the rust fungus Puccinia aethusae with consequent production of larger amounts of the toxins”
The sharp difference of opinion is disquieting. I have read many articles that claim a high level of toxicity but it is only the EFSA report that claims otherwise. So the EFSA is the outlier, and for now, I shall assume this plant to be toxic, especially from the evidence of the toxic chemistry (see below) and veterinary reports of poisoning of farm animals (although the point is sometimes made that toxicity disappears after hay-making).
The British distribution of Aethusa cynapium from BSBI/Maps. The higher resolution image on the right shows that it has retreated from many northern locations (pale colours represent older records) and is now recorded mostly in urban centres.
Despite having a reputation of being poisonous, it has been used in folk-medicine. The web-site Plants for a Future says “The herb is sedative and stomachic. It has been used in the treatment of gastro-intestinal problems, especially in children, and also to treat convulsions and summer diarrhoea”. Like many biologically-active compounds, it seems to be a foe or friend depending on the dose.
What are its poisons? The main toxic constituent is a long-chain alcohol, called Aethusanol. This resembles compounds found in the related genera Oenanthe and Cicuta (their similar toxins are called Oenanthotoxin and Cicutoxin). These molecular chains are made of linked carbon atoms, sometimes with double bonds, and with one or more hydroxyl groups (-OH) attached. Another toxic substance reported from this species is coniine, a completely different molecule found at higher concentrations in Hemlock, Conium maculatum.
Cicutoxin, found in several members of the Apiaceae, especially in Cicuta. It is C17H22O2. In this diagram, grey atoms are carbon, white are hydrogen and red are oxygen. Aethusanol is quite similar, but shorter and with only one -OH group. It is C13H14O.
The distribution map for the British Isles shows Fool’s Parsley to be declining, particularly in the northern half of Scotland. The reasons are unclear, but it is likely that a more-effective herbicidal weed control in arable fields is one of them.
For the world as a whole, the plant seems to have had quite limited mobility. In the case of North America, it may have been imported though confusion with Hemlock. An interesting but very old publication shows how pharmacists used Hemlock in the early part of the 20th Century and how they may have sometimes imported Fool’s Parsley by mistake (Ewing et al. 1912). This article also shows some early uncertainty regarding the toxicity of Fool’s Parsley.
Global distribution of Aethusa cynapium ssp. cynapium. Green shows the native range and purple is where the plant has been introduced and become naturalised. Note: in this map, Portugal and Iceland are not shown as part of the native range, but I think they should be. In Portuguese, the species is called Aipo-dos-câes. It’s in the Portuguese Infopaedia.
Here are some of the English names that A. cynapium has been given: Dog Parsley, Dog Poison, False Parsley, Fool’s Cicely, Fool’s Parsley, Lesser Hemlock, Small Hemlock.
References
Ewing CO et al. (1912) Conium maculatum L., and Aethusa cynapium L., an adulterant. The Journal of the American Pharmaceutical Association 8.5, 385-390.
Nelson LS et al (2007) Handbook of Poisonous and Injurious Plants, 2nd Edition. Springer
Stace CA (2019) New Flora of the British Isles. C&A Floristics.
©John Grace
Botany in Scotland 