Solanaceae offer feast or fatality

When Martyn Cox came across a plant growing on the headland of a potato field his curiosity was aroused. He dug it up, took it home and identified it as highly toxic henbane, one of several unsavoury members of the genus Solanaceae. ADAM CLARKE takes up the story.

Most of Britain’s arable fields are filled with a predictable range of crops and weeds, especially if you know the region like the back of your hand, so it came as a shock to find such an unsavoury weedy guest on the headland of a potato field in Norfolk this summer. After poking and prodding it, then pulling it up to take a sample home, the aforementioned weed turned out to be Hyoscyamus niger or henbane (pictured), a member of the Solanaceae family that is highly toxic.

Known also as stinking nightshade due to its pungent smell, it was made infamous by American homeopath Hawley Harvey Crippen who allegedly used hyoscine (an alkaloid extracted from henbane) to kill his wife in London in early 1910. In some cultures Henbane was used for ritual and recreational purposes due to its hallucinogenic properties, but it can also cause a wide range of unpleasant symptoms. These include dry mouth, thirst, difficulty in swallowing and speaking, warm flushed skin, dilated pupils, blurred vision and photophobia, vomiting, urinary retention…the list goes on. In severe cases, there may be hypertension, coma and convulsions or even death.

So why are some Solanaceae plants toxic? The 2,000-plus strong family is an unusual collection of species, containing some of the most harmful plants and some of the most widely consumed crops, including pepper, tomato, aubergine, potato and tobacco. All plants produce nitrogenous substances called alkaloids which can have significant physical effects on animals, even in small quantities. The Solanaceae are known to produce a particularly wide range of these compounds, including cholinesterase-inhibiting glycoalkaloids and steroid alkaloids.

Woody nightshade, Solanum dulcamara. Picture: Blackthorn Arable.

Woody nightshade, Solanum dulcamara. Picture: Blackthorn Arable.

These can be desirable to humans at low concentrations, with nicotine giving the stimulating, addictive effect of tobacco, while capsaicin gives chilli peppers their heat.  Nicotine is also found at low levels in potatoes, tomatoes and peppers and its purpose is to provide a natural defence mechanism against herbivores and insects – hence its use as an agricultural insecticide over many years.

Potatoes, aubergines and tomatoes contain solanine and although concentrations in tomato fruit and potato tubers aren’t harmful, they are known to cause gastro-intestinal disorders such as irritable bowel syndrome. Elevated levels of solanine in potato berries and green tubers left exposed to sunlight can, however, be very toxic and cause headaches, abdominal pain, shock and diarrhoea if eaten by humans.

Read the full article in our January/February edition

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