Plant Toxicity

Scrolling through Google news yesterday, I came across an item about a four-year-old girl in Bolton (a town in the north of England) who had brushed against giant hogweed and developed huge blisters on her hand. The photos looked pretty horrific – like huge water blisters as long as a finger joint.

So I read about Giant hogweed and it is a plant from the Caucasus that was was brought to Britain to Kew and distributed as an ornamental plant until its danger was recognised. It is recognised by the purple blotches on its stems and by its flowers that look like cow parsley. In ideal conditions the plant can reach five metres in height.

The sap of giant hogweed contains furanocoumarins. On contact with skin, these chemicals cause phytophotodermatitis. That is, the inflammation and blistering occurs after the plant is touched and is then exposed to sunlight because the furanocoumarins prevent skin from protecting itself from sunlight which then leads to bad sunburn.

Furocoumarins enter the nucleus of epithelial cells and form a bond with the DNA when exposed to UV light, and that kills the cell, and that causes inflammation. The chemical mechanism is known as the arachidonic acid cascade that involves prostaglandin hormones. They are found throughout the body and are involved in many inflammatory processes.

Certain furanocoumarins are toxic to fungi, which is interesting because of the role that fungi play in plant growth of very many other families of plants.

I went to the plant day at the Cambridge University Botanic Garden last Saturday and spoke with a researcher at the Cambridge University Department of Plant Sciences. She explained how most plant families regulate their intake of nutrients by a relationship with fungi in and around their roots and between plants.

The relationship, known as arbuscular mycorrhiza, is where a fungus penetrates the cells of the roots of a plant leading to a continuous orchestration of signals to benefit both the plant and the fungus.

The researcher explained that some plants – I think she mentioned the carrot family – do not have this relationship, and neither do plants that live in water.

That fits because Giant Hogweed is in the umbelliferae family of celery, carrot, parsley etc. Umbelliferae are easily recognised by the circular flower heads a circle made up of tiny flowers on short stalks around a central stalk.

This is a photo of umbels on a plant (NOT giant hogweed), to show how they look.


  1. John says:

    That’s really terrible, I hope the little girl will be okay! I have two Sago Palms in my backyard, they are nice to look at but very toxic to humans and pets. I have no pets…


    1. If she had a lot of contact, she might not fully recover because extensive contact can lead to damage to internal organs.

      Liked by 1 person

      1. John says:

        Oh my gosh, i had no idea obviously. Cut those things down, erradicate them.


        1. In the USA, giant hogweed is common alongside country roads and streams in New York State and it’s also in Virginia, Maine, Maryland, Michigan, New Hampshire, Ohio, Oregon, Pennsylvania and Vermont. In the UK it is found alongside the banks of streams and rivers more or less in the whole of the UK. I read that in the USA the plan to eradicate it is doing well, but there’s a lot to do.

          Liked by 1 person

        2. John says:

          I hope it is all destroyed…


  2. Joan E. Miller says:

    Ah, we have giant hogweed here in Washington state too. I wonder where it originally came from? I think I saw some in eastern WA. It does cause horribly painful rashes. We are supposed to report it when we find any.


    1. If you mean originally, It is native to Georgia, Southern Russia, and Southwest Asia. A 2018 article in the New York Times says it was brought to the United States for use as an ornamental plant around 1917.


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