Don’t be bitter: how to avoid toxic plants | Life and style


One of the most fascinating things for me as a greedy botanist is quite how different our most commonly cultivated crops are to their wild ancestors. Today’s sweet, seedless bananas are the result of an accidental sterile hybrid of two wild species that are so packed full of ball bearing-like seeds they are essentially inedible. The fat, juicy sweetcorn cobs we know from supermarkets started life as tiny sprigs of rock-hard seeds of a Mexican grass called teosinte. A totally different species. But perhaps the most extreme examples are crops like potatoes and squashes, whose wild relatives are packed so full of bitter toxins that it took thousands of years of selective breeding by farmers to make them edible.

The funny thing is, every so often, even some of our much-loved crops can revert without warning back to their wild, toxic ways, with potentially devastating effects. While cases are thankfully rare, the trend for saving your own seeds can pose a risk to home growers. So, here are three simple ways to keep safe.

Going rogue: wild relatives of some pumpkins are poisonous. Photograph: Flavio Coelho/Getty Images

Wild squash plants pack their fruit full of toxic, bitter-tasting compounds called cucurbitacins, which protect their seeds from predation. These can cause symptoms ranging from mild nausea and digestive discomfort to, in extremely high doses, death. While millennia of breeding work by indigenous farmers in the Americas has all but eliminated this from the breeding lines that resulted in today’s pumpkins, squash, courgettes and marrows, accidental crossing with other squash species can cause these chemicals to return. For growers in the UK, the key culprit is likely to be ornamental squash cultivars (the kind that grace Halloween flower arrangements), which are closely related, but full of the toxic compounds. In fact, as cucurbits are an extremely promiscuous family, even plants a significant distance away, say in neighbouring gardens or at the other end of allotments, can cause this accidental crossing. While the fruit themselves are extremely unlikely to be affected, seeds saved from otherwise perfectly tasty crops may indeed harbour the genes that contain the code for the toxin.

Fortunately, cucurbitacins come with a handy warning sign. They are incredibly bitter and so create a sensory warning sign that a plant is not safe to eat. For this reason alone, poisonings are fortunately rare, as few people tend to eat enough of the affected fruit to develop symptoms. So the moral of the story is simple: never eat any squash (homegrown or shop-bought) that has a strong, bitter taste.

Finally, aside from genetics, one of the triggers for cucurbitacin production is environmental stress. This can be triggered particularly by drought from irregular watering or a long storage period of courgettes in the fridge, so it pays to spoil your plants with water and keep an eye on how long they are stored.

I should make it clear, again, that incidences of poisonings are extremely rare, but as always it pays to know the risks, in order to keep your squash as tasty as they are nutritious.

Follow James on Twitter @Botanygeek

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