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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Tuesday 22nd May 2012

I spoke too soon. When I said Wednesday that my talks ‘season’ had ended I reckoned without getting a fairly short notice request to talk to a Rotary Club later this week.

It is an after dinner event with the request being for twenty minutes with no visual aids and I’m still trying to decide what to pick out for inclusion. The real skill, that I’m not sure I possess, is to say just enough to whet appetites so that there are plenty of questions at the end.

Urtica dioica, stinging nettle

Urtica dioica, stinging nettle

Regardless of the subject or the format, I start every talk with Urtica dioica, stinging nettle. It gets so many things on the table straightaway. Many people don’t think of it as a poisonous plant even though they know it causes pain so you are immediately into the difference between ‘poisonous’ and ‘deadly poisonous’.

The way it causes the sting is not what many people think so you get into false beliefs about plants and, in fact, the full mechanism of the stinging is still not understood so you can illustrate that our knowledge of how plants do what they do is incomplete.

Then there is the idea that rubbing a sting with a leaf from Rumex obtusifolius, dock, will cure it bringing up both the folklore of plants and the irrational beliefs people hold onto about ‘natural’ remedies.

And, I use stinging nettle to illustrate a key point about the use of potentially harmful substances. Since everyone knows that Urtica dioica will cause pain if given the chance, why do so many people give it the chance? Do they think it harms other people not them? Are they so desperate to get where they feel they need to go that they will accept the need to walk through a patch of nettles to get there? Do they convince themselves that the plants obstructing their path are actually Lamium orvala, deadnettle, rather than stinging nettles so there is nothing to fear?

Urtica dioica, stinging nettle

Urtica dioica, stinging nettle

And then there is what is known about how stinging nettle stings, a story dealing with the wonderful complexity of nature. Each of the tiny stinging hairs on the underside of the leaves is a sort of sealed hypodermic syringe consisting of a hollow needle with a brittle top and a bulb containing histamine, acetylcholine and 5-hydroxytryptamine. If you brush across the top of one of these hairs the top breaks off leaving a sharp end that sticks into the skin. The sideways action acts like pulling a lasso tight around the bulb so that the toxins are squeezed up the tube and into the skin.

The sideways movement seems to be an essential part of getting stung meaning there is some truth in the adage about grasping the nettle because, by so doing, you simply flatten the hairs rather than causing the tips to break off.

I’ve written before that many people say that the Romans introduced the stinging nettle to the UK but, as I pointed out, there is evidence that it was found in northern Europe long before the days of the Roman empire. I’ve just read another reference to it suggesting that it was found in what could be called Britain long ago.

Urtica dioica, stinging nettle

Urtica dioica, stinging nettle showing the
stinging 'hairs'

I’ve been reading the copy of Granta that Kris Hofmann was kind enough to send me. One of the pieces I’ve read, so far, is Robert Macfarlane’s account of a walk along a footpath in the sea off the coast of Essex. Macfarlane explains that during the last ice age so much of the earth’s water was locked up in glaciers that sea levels were over 100m lower than they are today. Off the Essex coast, this exposed a large area of land called Doggerland and studies of the seabed have shown that stinging nettles grew here ten thousand years before the Roman invasion.

It occurs to me that I could, probably, fill my twenty minutes just with the Urtica dioica but I don’t think that is what they want to hear about. We’ll have to see if I can make it teasing enough to ensure a question at the end.


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