Plants that … KILL!

Plants that kill: A natural history of the world’s most poisonous plants by Elizabeth Dauncey and Sonny Larsson, 2018. Kew Publishing.

When we think of plants – if we ever do(!) – it’s usually to consider the good that they do, e.g. in providing food, or medicines or clothing or building materials. Undeniably, plants do much good for us humans. But, there is – and always has been – a darker side to plants than we may care to realise. Plants produce a dazzling range of compounds, many of which we’ve discovered are quite poisonous and even fatal to humans. That mustn’t necessarily be interpreted as plants wanting to kill us – though goodness knows they’d have enough justification in holding that view given the ways that humans have used and abused them over the millennia! Rather, it’s a reflection of the complex world in which plants live and have evolved, and the need they’ve had to battle with and defend themselves against other biological entities. It truly is a jungle out there, and plants have had to arm themselves if they are to compete and survive. In that regard, humans poisoned and maybe even killed by plants – strictly speaking plant products not the plants directly – is just an example of ‘collateral damage’ in a war that the plants are generally fighting against non-human ‘aggressors’.

Well, and anyway, if you are a human, and keen to avoid being yet another casualty in the ancient battle between plants and other life forms, then Plants that kill: A natural history of the world’s most poisonous plants [hereafter called Killer Botanics] by Elizabeth Dauncey and Sonny Larsson may well save your life. Now that’s quite a claim for a book!

Although this is a large format book – the better to show off its wonderfully and colourfully, well-illustrated text – it’s a relatively slim volume at only 224 pages. It’s therefore not a comprehensive guide to all toxic plants or plant-derived compounds that could harm humans – or other life forms. It is therefore selective in what it contains. As stated in the Introduction, the focus is very much on flowering plants (although fungi get a mention where they exert their effects through close association with plants…), but with a global remit that describes a selection of those plants considered the most historically or culturally significant, interesting (!) and important in this regard. And it’s a most impressive selection. Yes, the ‘old standards’ that one might expect to see in such a collection – e.g. nicotine/tobacco, alkaloids/opium poppy, cardiac glycosides/foxglove, and cyanogenic glycosides/cassava – are there. But, there’s lots of other – and new – material too, to keep the reader “educated and delighted” (per the book’s Disclaimer on p. 4).

And the authors’ credentials for writing this book are impeccable. Dr Elizabeth Dauncey has spent many years working for the Poisons Unit of Guy’s & St Thomas’ Hospital in London, and is the author of Poisonous Plants: A Guide for Parents and Childcare Providers. Dr Sonny Larsson is a licensed pharmacist who latterly has worked for the Swedish Poison Information Centre, focusing on plant poisonings, herbal drugs and dietary supplements. The scholarship of those two individuals is therefore an assurance of the scientific value of the text, which should help to “educate, delight and expand the reader’s understanding of the diversity of plant life, the compounds they produce and their effects on animals and humans in particular”. The educational value of the text is provided by a great mix of plant chemistry (you really can’t avoid this entirely in such a book), medicinal consequences of the toxins, and human stories to illustrate some of the dangers of the compounds. The Kew dimension is also evident in that scientific names follow those from Kew’s Medicinal Plant Names Service, and species are assigned to plant families in accordance with the Angiosperm Phylogeny Group IV categorisation. You probably can’t ask for any more than that in terms of up-to-dateness from a taxonomy point of view.

One of the important features of the book – but which is not even hinted at by its more eye-catching, if rather sensationalist, title – is the fact that many of those otherwise human-health-harming poisonous plant compounds have been used by Mankind to actually help save or improve human lives. This duality of purpose of such plant toxins is highlighted in the cases of crocus-derived colchicine (e.g. for treating cardiovascular diseases and cancer); snowdrop-sourced galantamine (as a treatment for Parkinson’s disease), and curare, used originally in Amazonia to paralyse prey but which has been transformed into a powerful muscle relaxant for surgical procedures. Other plant-derived compounds have been exploited as agents in the battle against other life forms that in one way or another threaten humans or their lifestyles (the subject of chapter 10 “Turning foes into friends”). Justifying the book’s title, and seemingly needless to say, there are also examples of humans harnessing plant toxins to cause deliberate harm to other humans, e.g. alkaloids (from Indian aconite) used to poison the curry eaten by a love rival, ricin (from the castor oil plant) in the infamous ‘umbrella murder’ of ‘Bulgarian dissident’ Georgi Markov in 1978, and use of henbane-derived scopolamine by self-styled ‘Dr’ Crippen to murder his wife.

If your appetite for more toxic plants is well-and-truly whetted, why not consider also looking at Amy Stewart’s Wicked Plants: The A-Z of plants that kill, main, intoxicate and otherwise offend – which extends the range of Killer Botanics, and Cooper and Deakin’s Botanical Miracles: Chemistry of plants that changed the world – which looks at more than just harmful plants, but gives a great insight into the ever-expanding catalogue of plant chemicals? And, if you really are a ghoulish type, why not seek out and see for yourself, up-close-and-personal, some of the plants named in Killer Botanics by visiting such places as Alnwick’s plant poison garden* or the Royal Botanic Gardens at Kew? Just remember to wash your hands afterwards (and no taking ‘cuttings’!)…