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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Tuesday 27th September 2011

I’m working on a new page for the A to Z section about Rhododendron. (UPDATE; the page is now available here) It is not an especially poisonous plant, in fact, it isn’t included in the Horticultural Trades Association (HTA) list of potentially harmful plants. This is the list that forms the basis for Dr Elizabeth Dauncey’s book ‘Poisonous Plants – A guide for parents and childcare providers’.

But, it is poisonous and there is a particular situation with the nectar of the plant that leads to some of the exaggerated stories about the harm that is caused as so often happens with poisonous plants. My problem, so far, is that I’m not too sure how interesting it is.

The Rhododendron is a native of southern Europe all the way from Spain in the west to Turkey in the east. In those areas stories about the effects of the toxic nectar date back to about 400BC but it was unknown in the UK until the 18th century. John Gerard, for example, has no mention of it.

Rhododendron

It is said that the first Rhododendron ponticum was introduced to the UK in 1763. Like a lot of non-natives, it took to its new home and soon began to colonise whole areas where just a few plants had been introduced. Today, you will often hear that Rhododendron ponticum is a serious problem but that is almost certainly untrue.

I don’t mean that large swathes of Rhododendron aren’t extremely troublesome. I mean it is very unlikely to be R. ponticum. Rhododendron is thought to appear in around 1,000 species and those species produce innumerable hybrids. This means there are very few people expert enough to identify exactly what Rhododendron a particular plant is.

In terms of appearance and flowering, that doesn’t matter too much but it has been found that the concentration of the main toxin is species/hybrid dependent so plants that appear to the layman to be identical may produce different degrees of poisoning.

In general, it is the toxic nectar that continues to attract most of the interest and the difficulty of distinguishing exactly which species or variety of Rhododendron is what leads to confusion between bee-keepers when they find that bees are dying from visiting Rhododendron bushes ‘exactly the same’ as other bushes that have produced no ill effects.

Of course, it is the question of whether toxic honey gets consumed by humans that is of most interest to the majority. It seems unlikely. First of all, as above, bee-keepers know that their bees are visiting Rhododendron when significant numbers die. Obviously, these dead bees don’t make it back to the hive to unload their toxic cargo. In areas where there can be high concentrations of flowering Rhododendrons, bee-keepers are reported to keep their hives closed until the danger passes.

Rhododendron

Then there is the question of how bee-keeping works. Nectar collected early in the year, and Rhododendron are often the first bushes in flower, is often retained to feed the hive and it is not until later in the summer that honey is removed.

Then there are those who say that the toxin, variously called andromedotoxin, grayanotoxin, rhodotoxin and acetylandromedol, decays with time in honey so that by the time honey is consumed the level of toxicity is negligible. And honey with a high level of toxins from Rhododendron is said to be unpleasant to the taste though not, perhaps, as unpleasant as honey made exclusively from Jacobaea vulgaris, common ragwort, as there have been reported cases of honey poisoning.

So, there’s quite a bit of fact about the toxicity of Rhododendron and some of the claims made about the harm arising from honey belong in the fiction category. What I don’t have much of, so far, however, is folklore. Being such a newcomer to the UK it hasn’t developed any UK-based folklore and it doesn’t seem to have much in its native lands other than a vague notion that it is ‘protective’ against evil.

What started me thinking about creating a page was a news story, today, that the National Trust are close to completing a project to clear Brownsea Island in Dorset of Rhododendron in order to have a safe habitat for one of the few colonies of red squirrels to be found in England. We usually think of the grey squirrel as being the foreigner endangering the survival of the red. On Brownsea Island, however, the foreigner is a plant that more or less took over completely leaving no habitat for the red squirrel.  

It’s a stark lesson in the effects of invasive species to learn that the work on Brownsea has taken fifty years to complete.

 

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