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Author Topic: Why are rhubarb leaves poisonous?  (Read 62844 times)

Paul Anderson

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Why are rhubarb leaves poisonous?
« on: 08/10/2008 09:55:39 »
Paul Anderson  asked the Naked Scientists:

Hi Chris and team,

As a lad I was always told that rhubarb stems could be eaten but the leaves were poisonous.  Why is that?  The plant grows up from the ground and the leaves are the furthest from its source of origin.  I would have thought that the poison would be in the stems and might be less likely to reach the leaves.  Is it a poison which interacts with chlorophyll?

Is it the cooking which breaks down the oxalic acid in the stems? Did they only realise that the leaves were poisonous during WWI when there was a lack of vegetables?
 
Regards
Paul
NZ

What do you think?

JnA

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Why are rhubarb leaves poisonous?
« Reply #1 on: 08/10/2008 14:03:44 »
I would think that the leaves would be the first thing critters would try to eat, makes sense to make that *more* poisonous.

I believe it was a WWI discovery indeed.

Don_1

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Why are rhubarb leaves poisonous?
« Reply #2 on: 08/10/2008 14:17:23 »
The leaves and even the stalks contain Oxalic acid. This is lower levels in the stalk than the leaf and nowhere near enough to be dangerous. The Oxalic acid in itself is not a problem, but the leaves also contain Anthraquinone Glycosides. It is thought that the combination of the two may be the reason for the leaves to be poisonous.

Why is this Anthraquinone Glycoside found in the leaf and not the stem? I can only assume that it is not produced in the root or stem, but only the leaf. There are many plants which produce toxins in the leaf for protection against insects and insect larvae.

blakestyger

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Why are rhubarb leaves poisonous?
« Reply #3 on: 08/10/2008 18:16:42 »
There are many plants which produce toxins in the leaf for protection against insects and insect larvae.

That's right, and I thought that applied to rhubarb - until last summer (and this) when we had leaves that were eaten right down their ribs! So something can get past its defenses.

Bored chemist

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Why are rhubarb leaves poisonous?
« Reply #4 on: 08/10/2008 18:46:42 »
I think the anthraquinone derivatives are found mainly in the roots.
The real question is how did anyone find that "that pink bit in the middle" is edible?

blakestyger

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Why are rhubarb leaves poisonous?
« Reply #5 on: 09/10/2008 08:08:50 »
It's a bit like the variety of potato found in the Andes that can only be eaten if they're cooked after being urinated on and left out in a frost. :0 How did they find that out?

Bored chemist

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Why are rhubarb leaves poisonous?
« Reply #6 on: 09/10/2008 18:38:05 »
How do you normally cook potatoes?

blakestyger

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Why are rhubarb leaves poisonous?
« Reply #7 on: 09/10/2008 21:30:32 »
How do you normally cook potatoes?

Come again. ???

rosalind dna

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Why are rhubarb leaves poisonous?
« Reply #8 on: 09/10/2008 22:03:36 »
Yes Rhubarb leaves are poisonous unlike the rhubarb sticks, so
are raw potatoes poisonous as are the green bits of potatoes.

I don't think that the chlorophyll has anything to do with it as
we eat lettuce, greens. cabbage and other green (chlorophyll) veg minus harm.

Don_1

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Why are rhubarb leaves poisonous?
« Reply #9 on: 10/10/2008 16:42:08 »
There are many plants which produce toxins in the leaf for protection against insects and insect larvae.

That's right, and I thought that applied to rhubarb - until last summer (and this) when we had leaves that were eaten right down their ribs! So something can get past its defenses.

The problem with many plant toxins is that some bugger will develop a way of passing them through the body without effect, or even utilising them to their own advantage. The Red Admiral Caterpillar utilises the sting from stinging nettle. But one very ancient plant, Bracken, has developed a toxin which no animal, insect or their larvae can eat without effect.

blakestyger

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Why are rhubarb leaves poisonous?
« Reply #10 on: 10/10/2008 17:36:21 »
Yes Rhubarb leaves are poisonous unlike the rhubarb sticks, so
are raw potatoes poisonous as are the green bits of potatoes.

I don't think that the chlorophyll has anything to do with it as
we eat lettuce, greens. cabbage and other green (chlorophyll) veg minus harm.

The green bits in potatoes are chlorophyll and, as you say, it's harmless but it indicates the presence of solanins that are mildly toxic - to the extent it will cause stomach upsets.

Bored chemist

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Why are rhubarb leaves poisonous?
« Reply #11 on: 11/10/2008 12:22:04 »
It's a bit like the variety of potato found in the Andes that can only be eaten if they're cooked after being urinated on and left out in a frost. :0 How did they find that out?
How else does one prepare spuds? I thought this was the only way.

Bored chemist

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Why are rhubarb leaves poisonous?
« Reply #12 on: 11/10/2008 12:25:31 »
There are many plants which produce toxins in the leaf for protection against insects and insect larvae.

That's right, and I thought that applied to rhubarb - until last summer (and this) when we had leaves that were eaten right down their ribs! So something can get past its defenses.

The problem with many plant toxins is that some bugger will develop a way of passing them through the body without effect, or even utilising them to their own advantage. The Red Admiral Caterpillar utilises the sting from stinging nettle. But one very ancient plant, Bracken, has developed a toxin which no animal, insect or their larvae can eat without effect.
Sure about that? see the 3rd paragraph here
http://www.apstas.com/bracken.htm

Don_1

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Why are rhubarb leaves poisonous?
« Reply #13 on: 12/10/2008 09:45:52 »
Bored Chemist

Well I am amazed and stand corrected.

Karen W.

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Why are rhubarb leaves poisonous?
« Reply #14 on: 12/10/2008 13:24:24 »
This is good information. I really love taw rhubarb when it is ripe!

 My grandparents grew Rhubarb for years and always told us that the whol rhubarb plant was toxic untll certain part of the season when it redened up just right, but tht the leaves remained poison all  the time ..... So what I have ben taught is really not accurate eh??? not seasonally poison?.. Thanks guys!

Bored chemist

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Why are rhubarb leaves poisonous?
« Reply #15 on: 12/10/2008 15:16:41 »
Bored Chemist

Well I am amazed and stand corrected.
It's seldom a good bet to say that "Living things cannot do such and such". A few billion years of evolution has taught it practically every trick you can think of and then some.

blakestyger

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Why are rhubarb leaves poisonous?
« Reply #16 on: 12/10/2008 18:13:13 »
Bored Chemist.

Interesting about the bracken. I have heard that the Japanese are very fond of eating the young croziers and that this has been linked to high incidences of stomach cancers.

Make it Lady

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Why are rhubarb leaves poisonous?
« Reply #17 on: 12/10/2008 20:08:35 »
How do you normally cook potatoes?

Come again. ???
you don't have to do that on them as well do you?

Make it Lady

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Why are rhubarb leaves poisonous?
« Reply #18 on: 12/10/2008 20:13:22 »
Bored Chemist.

Interesting about the bracken. I have heard that the Japanese are very fond of eating the young croziers and that this has been linked to high incidences of stomach cancers.
My Dad never let us touch bracken when we were young. I never understood why but he always said that it was something on the bottom of the leaf?!

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Why are rhubarb leaves poisonous?
« Reply #19 on: 13/10/2008 18:20:32 »
The spores of this fern are stored on the bottom of the leaf. They are dark brown and very small.
They are certainly messy, they are probably allergenic and they may well contain high levels of ptaquiloside.

Don_1

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Why are rhubarb leaves poisonous?
« Reply #20 on: 14/10/2008 15:52:31 »
How do you normally cook potatoes?

Come again. ???
you don't have to do that on them as well do you?

Well if nobody else spotted this, I did!!!

Shame on you............... I SAID SHAME (before you make any other suggestions)

BenV

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Why are rhubarb leaves poisonous?
« Reply #21 on: 14/10/2008 17:17:22 »
I think everyone else was too polite (or too embarrassed) to comment!

Madidus_Scientia

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Why are rhubarb leaves poisonous?
« Reply #22 on: 28/11/2008 11:29:34 »
again!?

CliffordK

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Why are rhubarb leaves poisonous?
« Reply #23 on: 18/08/2011 04:53:26 »
Something defoliated my Rhubarb the night before last.

Fortunately it ate the leaves and left the stems.   :D

I don't see any dead animals in my pasture, but I'm hoping it got a good stomach ache   xx(

I tried tasting the leaves (just to see)...  and they tasted much more bitter than the plant itself.

 

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