Monday, October 5, 2009

The Alien that Conquered Britain


The conker season is here again – amply celebrated today in an article in the Times newspaper (see http://www.timesonline.co.uk/tol/news/uk/article6860922.ece). Horse chestnut Aesculus hippocastanum is our best-loved alien species which, during the 400 years since it was first introduced into Britain from the Balkans, has graced our parklands and become the focus of a traditional sport that has left generations of school-kids nursing aching knuckles after misjudged swings of an opponent’s conker.


The seeds of horse chestnut are truly exquisite objects. Their deep umber hue has given its name to a colour and their glossy texture contrasts wonderfully with the spiky husk that they are enclosed within. Sadly, it’s a beauty that doesn’t last – after a day or two those glossy seeds become leathery and lose their rippled patterns. In the USA Aesculus species are known as buckeyes, on account of the resemblance between those glossy brown orbs and the eyes of deer.



I may be wrong, but I suspect the horse chestnut seed is the largest amongst trees in Britain. They invest a lot of resources in giving their germinating seeds the best possible start in life, by providing them with a very large food store.... but at the expense of long-distance dispersal (take a look at http://beyondthehumaneye.blogspot.com/2009/10/travelling-light.html for a completely different plant seed dispersal strategy).


One of the perils of producing seeds with a large food store is that they simply become food for hungry animals (think of all the acorns that are guzzled by squirrels, jays and wood pigeons) - which may be why conkers contain high levels of toxic substances called saponins which are natural detergents and generally damaging to animal digestive systems. Ground-up conker flesh can provide a deterrent against slugs, which have a strong aversion for saponins and tend not to cross a barrier of conker meal. This might be the basis for a natural method of slug control, but for the fact that saponins are water soluble, so that any attempt to use them as slug deterrents would be washed away in the first shower of rain.

18 comments:

  1. Once again I've learn't. Thanks that's about quadrupled my knowledge of the Horse Chestnut.

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  2. Love that tabloid title Phil lol
    Interesting read about the toxic content. Never knew that.
    I tried a couple of years ago to get some decent pictures of conkers, and failed miserably. Yours are great; and that last one a real conqueror.

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  3. I didn't know about the toxic content either.
    There are quite a few Horse Chestnut trees in the village. Walking the pavements under them is like walking on a pebble beach at the moment. There seems to be a bumper crop this year.

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  4. Hi Adrian,the gales last weekend brought a lot of conkers down and I just can't resist picking them up!

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  5. Thanks Keith, if I'd had one I would have used a polarising filter to get rid of the highlight/reflection

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  6. Ho John, we seem to have a good crop here this year, although not many really big ones. The horse chestnut leaves seemed to turn yellow very early this year, maybe because it has been so dry up in Durham..

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  7. I've not see that spelling (hypocastanum) before but I see that it is used in many places, though not as much as hippocastanum. And I've found one site that uses both! Now I am confused.

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  8. Excellent post and some wonderful shots. Have any of the trees up here been affected by the disease which appears to be spreading to Chestnut trees in southern Britain? The trees around Morpeth seem to be fine.

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  9. Dougie, you are absolutely right - a typo on my part - thanks for pointing it out! It should be Aesculus hippocastanum.

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  10. Hi abbey meadows, I'm told the insect that's causing the problem - a leaf mining moth called Cameraria ohridella - has now reached North Yorkshire. I saw a lot of trees infected with it in Kings Lynn in the summer. Give it a year or two and I think it will reach us.

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  11. They are such beautiful things and a good example of how easy it is to take the commonplace for granted.
    Now I think about it, I'm puzzling how the tree get its seeds dispersed (other than by small persons). If they aren't attractive to animals as a food source then presumably they won't get carried off - like acorns do- an scattered that way?
    Also, the edible sweet chestnut, which is superficially very similar, hasn't developed such a poisonous defence. It must have a different mechanism, I suppose?

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  12. Ah! I remember those stinging knuckles! Hadn't thought about them in over 40 years. As a lad in the colonies (Canada) in the 50s and early 60s, whacking chestnuts (or conkers, as you call them) was a popular fall pastime. I remember the pride of owning a champion, which I retired undefeated after 20-some battles.

    Wonder where it ended up?

    Thanks for the memory jog. This looks like an interesting blog. I suspect I'll be back. :)

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  13. Hi Nyctalus, interesting point...in evolutionary terms the two species aren't closely........ although they have similar English names their biochemistry could easily be unique

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  14. Greetings Frank... and thanks for your kind comment. Regrettably the Health and Safety Policy frown on the game these days .... see http://news.bbc.co.uk/1/hi/education/1060708.stm

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  15. On the other hand :-)
    http://www.hse.gov.uk/myth/september.htm

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  16. The chestnut pictures are beautiful, Phil. Lovely light and colour.

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  17. Point taken,Nyctalus... I guess its fear of litigation from parents and ambulance-chasing lawyers that's the real blight

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  18. Thanks Emma, I find that lovely rippled pattern particularly attractive.

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