Return of the giant hogweed

'Turn and run! Nothing can stop them. Around every river and canal their power is growing.' Funny, but it has never occurred to me before now that Peter Gabriel's apocalyptic, if rather fanciful, lyrics to The Return of the Giant Hogweed (Nursery Cryme 1971) are about the true story of the introduction of the plant to the Botanic Gardens at Kew during the great age of Victorian acquisitiveness, and its inevitable consequences. In Gabriel's re-telling the giant hogweeds take on the guise of John Wyndham's triffids, bent on vengeful human annihilation.

Giant hogweed by the river Esk

Last week I was writing about our harmless native hogweed. Today, walking the river Esk in East Lothian, I came across an immense infestation of giant hogweed, Heracleum mantegazzianum, an altogether more frightening encounter. There were many specimens of easily twice my height and the large area, completely overrun by the plant, was sealed off behind barbed wire. And for good reason... giant hogweed is best given a wide berth.

The plant produces a sap which reacts with ultraviolet light. Even mild contact such as brushing against the hairy stems can leave the skin hyper-sensitive to sunlight, resulting in painful and persistent blistering that may recur for years. The giant stems are hollow, making them attractive for children's games as swords, blowpipes or telescopes, with potentially horrible consequences. There are cases of hospitalisation every year.

As Peter Gabriel laments, giant hogweed, which originates from the Russian Caucasus, is virtually indestructible, requiring a co-ordinated effort by landowners, local authorities and environment agencies over a many years. According to East Lothian Council's website, council officers are engaged in a long-term campaign of eradication, backed by legislation making it an offence to plant giant hogweed or to allow it to grow unchecked on private land.

Sandra has written recently about the tenacity of weeds and the futility of our attempts to submit them to our will. Readers of my earlier posts will know that I, too, am an admirer of the weed. I am left with a sense of deep ambivalence about plants like the giant hogweed and Himalayan balsam and others. After all, we reap what we sow. Brought to Britain as ornamental curiosities, they are one legacy of the colonial hubris of our ancestors. In spite of all our best (and costly) efforts at eradication they are almost certainly here to stay. Containment through responsible environmental management is probably the best we can hope for.

Let me stress I have absolutely no wish to see children blinded or disfigured through contact with this plant, any more than I would want to see people bitten by adders, poisoned by mushrooms or injured by any other agent of our natural world. In that sense we are fortunate in Britain that there is not much out there to do us serious harm. But in our enlightened twenty-first century do we still entertain the eradication of species on the grounds that they are potentially harmful to us, our pets or our livestock? What is missing from East Lothian Council's website is surely what should be the second prong of its campaign, education. There are no photographs or drawings by which to identify the plant, no advice for parents or gardeners on avoiding contact or what to do if experiencing symptoms. We must kill it, that is all.

The giant hogweed is undoubtedly impressive although not especially attractive. It is certainly a plant to be treated with extreme caution. On balance it would probably have been better if Victorian gentlemen collectors had not brought it here. But they did and we must learn to live with it as we must the grey squirrel, the sycamore, the mink, the rhododendron, the New Zealand flatworm and the myriad other newcomers to our islands. We should remember that unlike John Wyndham's sci-fi triffid, the giant hogweed isn't an invader, we introduced it.

Knowing your umbels

It has been a soggy June north of the border, following on from one of the wettest Mays on record. Parts of west Scotland recorded rainfall levels of 250% the monthly average. Watching news coverage of parched earth and stunted cereal crops in East Anglia it is sometimes hard to credit we live in the same small isle. On the plus side, nothing grows without rain and it has been a season of rampant growth. Hedgerows, meadows and lanes are ablaze with wild flowers and it is hardly possible to go for a country walk without wading through a strangle of brambles and nettles and tall stems of hogweed with its profusion of white and pinkish flowers.

The unkindly named hogweed is a member of the carrot family, a very large group of mostly white or yellow flowering plants which includes many important culinary species like chervil, cicely, caraway and angelica and others with medicinal properties. Many of them grow to a great size, none more so than hogweed which often reaches shoulder height. The giant hogweed, not native to Britain although widespread here, may tower to ten feet or more.

Typical flat topped umbel of common hogweed

Like most of the carrot family, common hogweed or Heracleum sphondylium bears its small flowers in spoked clusters called umbels (think umbrella). These may be the breadth of a hand span and are typically flat topped and borne high about the stout hollow stems. For novices like myself telling umbelliferous plants apart can be confusing as they may be very variable and the individual flowers are often indistinct. Usually the shapes of the leaves give better clues and fortunately they often grow together, making for easier comparison.

And identification is important, for mixed in among these aromatic herbs and also bearing white umbels are some of the most poisonous plants to be found anywhere, the hemlocks and water dropworts, which are potentially lethal to humans and livestock alike even in comparatively small doses. Some of them are all the more dangerous for being common and all parts of the plants are toxic; leaves, seeds and especially roots. Hemlock poisoning, which causes respiratory paralysis while still conscious, was apparently a favoured means of execution in classical Greece. Its most celebrated victim was Socrates, put to death for his outspoken criticism of Athenian democracy, whose demise is told of by Plato in the Phaedo.

Outermost flowers of each cluster are larger

Common hogweed isn't poisonous, nor is it something you would probably want to try to eat, but it does have a taxonomic name with classical associations, Heracleum. I wonder whether this is simply a reference to its size or whether like Achillea, the yarrow - which Greg wrote so interestingly about- there is some other significance that I am missing.

It is fairly straightforward to identify from the flowers alone. They are often pink when still buds, the ones in the centre of each umbel being the last to open. There are five petals and flowers at the outer edges of the cluster have a pair of larger petals, projecting outwards, shaped rather like miniature fish tails. The flowers are much frequented by insects including bees. They give off a mildly unpleasant scent which I have only really noticed on hot, muggy days when the flowers are very abundant. Hogweed's attraction of insects potentially makes it a valuable companion plant for crops because it may aid pollination or pest control. Certainly it is often found around field edges but I think it unlikely that its seeds have been sown purposely as it is naturally invasive.

I don't suppose hogweed will feature high on the list of favourite wild flowers for many people and I must count myself among them. But I associate it with countless country walks on summer days when the sky is blue and the air is hot and fizzing with insects. And in our current, decidedly unspectacular Scottish summer, that surely can't be bad.