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Saturday 28th April 2012

Everywhere is looking very yellow at the moment. In the fields it is the flowers of Brassica napus, oilseed rape, giving a golden sheen to large swathes of countryside, especially in the brief moments when the sun comes through between the rain clouds.

And, on the roadside verges, it is Taraxacum officinale, dandelion, replacing the yellow Narcissus, daffodils. I can’t claim to have made a careful study, but it does seem that there are an unusually high number of dandelion flowers this year. The question, for me, is – does dandelion count as a poisonous plant?

Taraxacum officinale, dandelion on a roadside
verge

There is plenty of folklore associated with Taraxacum officinale though, as often happens, if it were all true it would have some unfortunate outcomes. Once the bright yellow flower has been pollinated it produces a sphere of light seeds designed to be blown on the wind to distribute them. In some cultures, it is believed that you can use blowing on the seeds to indicate true or false love much as you would with daisy petals. So, odd number blows mean ‘he/she loves me’ and even is for ‘he/she loves me not’. The number of puffs needed to blow every seed from the stalk being the decider.

Others believe that dandelion can be used to tell the time because the number of puffs to reach bare stalk is the number of hours past the twelve. Dandelion, apparently, doesn’t do the 24 hour clock.

But for either of those folkoric uses, you need to pluck the dandelion off the plant to bring it to your lips and that’s where the problem comes. Like most plants Taraxacum officinale has a number of common names. Such names are often related to the look or properties of the plant. So, in French, dandelion is called pissenlit but, in English, rather than a fully literal translation it is known as pisse-a-bed. This is because picking the flower will result in a nocturnal accident.

Although John Gerard uses that name, he doesn’t describe it as a diuretic when detailing its ‘virtues’. Rather he talks of it causing constipation and, therefore, being a remedy for dysentery. That contradicts its use in Jordan, even today, as a cure for constipation but I’ll return to Jordan in a moment.   

Taraxacum officinale, dandelion

Use of dandelion as a diuretic is found in the 10th century in Arab medicine and it may have found its way into European use from there. Excessive use of a diuretic can lead to a loss of minerals in the body and produce a variety of medical problems so, simply being a diuretic, would be enough to be able to label Taraxacum officinale as a poisonous plant.

In spite of its long use for this purpose, however, there is still no reliable proof of this property. In fact, at least one study found an absence of any effect on urination.¹ There was a 2009 ‘pilot study’ that claimed to find diuretic effects in 17 subjects². Pilot studies are supposed to be about proving a method and are, therefore, too small to produce reliable results. Also, there is no indication of any blinding in the study. Though I know nothing about this particular work, there have been cases where people have taken pilot study results and claimed them as complete proof.

At this time, therefore, there remains no reliable indication of any chemical diuretic effect and, if there is no effect, then there can be no risk of overdose.

But it is not just as a diuretic that dandelion might work on the body. In Jordan, as well as being used to treat constipation, dandelion is used to boost male fertility. A study in rats, however, found that rather than enhancing fertility, regular doses of dandelion damaged testes size and sperm count³. I can’t tell from the extract whether the amounts given to the rats bear any relation to the sort of amounts a normal male might consume.

Taraxacum officinale, dandelion

Other recent work has suggested that it may have a role as a chemotherapy agent⁴, though it is not clear whether it has any benefits over current treatments that might justify further study. Chemotherapy, of course, is a form of controlled poisoning.

But nothing really explains how it came to be used as a diuretic and whether it should be called a poisonous plant. It may just have been one of the plants that became associated with increased urination. Somewhere, I have a list of over 1,000 plants that have been, at some time in history, prescribed as herbal remedies for rheumatism and there may be a long list of alleged diuretic plants.

Or, the yellow colour of the flower may have created the belief that it would have an effect on yellow bile production.

Plants in the Taraxacum genus are, generally, described as edible but it does come within the Asteraceae family that contains some well-known poisonous plants. It seems overall you might be able to stretch the definition to include dandelion as poisonous but it hasn’t been found to be harmful in everyday circumstances.

How we classify plants is, often, a subjective matter rather than being wholly based on evidence.

References

^1.Evaluation of Dandelion for Diuretic Activity and Variation in Potassium Content Pharmaceutical Biology 1993, Vol. 31, No. 1: 29–34. 
^2.The diuretic effect in human subjects of an extract of Taraxacum officinale Folium over a single day Journal of alternative and complementary medicine (New York, N.Y.). 09/2009; 15(8):929-34.
DOI: 10.1089/acm.2008.0152   
^3.Dandelion (Taraxacum officinale) decreases male rat fertility in vivo. Journal of ethnopharmacology. 02/2011; 135(1):102-9. DOI: 10.1016/j.jep.2011.02.027
^4.Efficient induction of extrinsic cell death by dandelion root extract in human chronic myelomonocytic leukemia (CMML) cells. PLoS ONE. 01/2012; 7(2):e30604. DOI: 10.1371/journal.pone.0030604

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