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Phuket Gardening: Lovely but lethal tropical plants

A reader recently wrote to me about the poisonous propensities of the nerium or oleander. I replied, noting how the goats tethered next door to my garden in Spain – and goats will eat almost anything – had always refused to touch my oleander hedge.


By Patrick Campbell

Saturday 9 December 2017, 10:00AM


Quite properly, the writer wanted to remind us about the shrub, citing the case of a family who became seriously ill after inhaling smoke from a bonfire containing oleander branches. Highly poisonous. Even the latex can give you a nasty rash.

Of course, when you are stocking a garden, one of many decisions facing you may be about growing poisonous shrubs. It is of course a personal choice and may well depend on whether or not you have young children or pets.

But one of the more extraordinary facts about tropical plants is that they are, for the most part, either toxic or edible. Some food plants here, like cassava for example, have it both ways: they are both poisonous when raw, and safe to eat when cooked.

On the other hand, those of us who come from temperate climes know that not many wild fruits are seriously edible, apart from blackberries and a range of autumnal nuts (at a pinch you could include crab apples, sloe berries and hips).

But we also know that little we encounter will be seriously poisonous, apart from the glossy purple berries of the deadly nightshade (Atropa belladonna). And while other toxic plants such as the foxglove (digitalis) or members of the wolfsbane family, as well as deadly fungi such as the fly agaric, do indeed exist (even the humble buttercup and cowslip can be harmful if ingested), we are unlikely to sample them in a salad.

Not so in Thailand. Lost in a rainforest, you would hardly die of starvation: many of the hybrid plants we now cultivate – bananas, mangoes, sator, breadfruit, tamarind – have always existed as species in tropical jungles. If you could know which ones were edible, you could even survive on leaves. But you could also die, and not just from a cobra or krait bite, but from ingesting the wrong bits of the wrong plant.

To return to the oleander. A member of the apocynaceae or wolfbane family, most are toxic, including two of my favourite plants: Allamanda cathartica (yellow trumpet), and Thevetia peruviana (yellow oleander). Both contain indoid lactone, a potentially fatal cathartic. If you do decide to grow them – as I have – remember to avoid contact with the milky latex when you prune the shrub’s excesses, dispose of the large green drupes of Thevetia, and refrain from making a bonfire of cut branches.

Another plant to be careful of is the elephant’s ear or caladium. This massive member of the araceae clan grows everywhere in Thailand where there is moisture and shade. Literally thousands line the mountain road between Kata and Rawai. I once planted a number in my new garden in an endeavour to create instant patches of shade – a tactic doomed to failure, since their natural habitat is marshy jungle. But elephant’s ears are also poisonous and if you cut off those dramatic, sail-like leaves, remember to wash your hands lest you come out in a rash.

Many other understorey plants from tropical forests, usually smaller, are grown commercially, both in European hothouses and under plastic netting in Thai garden centres. Many are poisonous, partly as a defence against the jungle’s browsing animals. For example, the heart’s leaf philodendron contains calcium oxalate; others, potent alkaloids.

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Appearances are deceptive. The Madagascar periwinkle (Catharanthus roseus) is a charming little flower related to the indigo blue vinca that lights up European hedgerows. Its pink or white flowers are a familiar presence here: it flourishes in the most unlikely sandy and saline soils. It looks harmless enough, but its glossy leaves contain those very same alkaloids. Odd then that oleander hawk moth caterpillars feast on its foliage.

But the most toxic plant of all is the innocuously named castor oil plant or Ricinus communis. I innocently grew several large specimens in my London garden; even now, my ex-wife has a splendid array in pots on her city balcony.

But without wishing to sound alarmist, the purplish-black berries contain ricin, one of the deadliest poisons known to man, and one used – notoriously – to assassinate Georgi Markov in 1987.

Of course toxic plants are not without their attractions to humanoids as well as caterpillars. As well as looking splendid, a significant number produce hallucinogenic effects when ingested in small quantities – morning glory, brugmansia, and lots more I had better not mention.

But significantly, the chemicals in most of these poisonous plants also provide treatments for all sorts of ailments. The pharmaceutical industry is at last waking up to their huge potential for good.

It is always worth remembering that our gardens are probably more hazardous than we think… Just ensure your children or pets don’t try out these plants.

 

Patrick Campbell has been writing for ten years about gardening in Phuket and allied topics. If you have questions, please contact him at drpaccampbelll@gmail.com or visit his Wordpress blog: Green Galoshes.

 

 

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