Two or three years ago I received an email telling people to get rid of a certain plant, as it was so poisonous it could kill a child "in less than a minute and an adult in 15 minutes". It added that if the plant is touched, "One should never touch one's eyes; it can cause partial or permanent blindness." The plant was not named, but the message showed a picture of a dieffenbachia.
CARE AND CAUTION: Plumeria, allamanda and poinsettia all yield a milky sap which can cause skin irritation if not handled with care.
That warning is back in circulation, this time on Facebook, and after reading it I am sure many people who do not know much about plants will be discarding this beautiful plant from their gardens rather than compromising their safety or that of their children and pets. It is true that the dieffenbachia has been given the common name "dumb cane" because its leaves and stems contain calcium oxalate crystals which, when ingested, can cause temporary paralysis of the tongue, making speech intensely difficult for some time. There is no record, however, of anyone being killed or blinded just by touching it _ so the warning being circulated on social media is clearly a hoax.
When my children were growing up, their father saw beauty in the palmate leaves and thorny fruit of the castor bean. He grew it right in front of our house. The seeds of this shrub are the source of purgative castor oil, but contain the dangerous substance ricin _ and when ingested, the effects are similar to that of a snake venom. If a toxic dose is ingested (and a lethal dose can be as few as four to eight seeds), it may be at first asymptomatic except for a loss of appetite; however, it can be followed by intense diarrhoea, delirium and even death if medical attention is not given. But the mere handling of the seeds, even with bare hands, is totally safe.
Most plants which secrete a milky sap must be handled with care. Yellow oleander (Thevetia peruviana), known in Thai as ramphuey or naree ramphueng, is a beautiful shrub with bell-shaped yellow or orange flowers and small, four-sided green fruit with nut-like seeds. But all parts of this plant contain a substance called thevetin, which is poisonous if ingested.
THE GRAPEVINE: The toxicity of the dieffenbachia is the subject of a hoax currently being circulated on Facebook.
The symptoms of poisoning include a slow and irregular pulse, which can be followed by vomiting and finally toxic shock.
Thevetia peruviana belongs to the Apocynaceae family of plants _ whose other members, Nerium oleander, better known simply as oleander and not to be confused with the yellow oleander, and Allamanda cathartica, or simply allamanda _ contain poisonous substances in their milky sap. Oleander, or yeeto in Thai, is an evergreen shrub with attractive single or double flowers that range in colour from yellow and yellow-orange to pink and dark-pink, but all parts _ flowers, leaves, stems and roots _ are extremely poisonous if ingested. The sap of both the oleander, and the allamanda, known in Thai as banburi, can cause irritation if handled with bare hands. Special care must be given if you have an abrasion on your hand, as the poison could get into your system through the open wound.
Strangely enough, I have seen caterpillars feeding on the leaves of the oleander. They have developed immunity to the plant's poison, the same way as the clown fish is immune to the sting of the anemone; birds know instinctually to avoid eating caterpillars that feed on the poisonous plant.
However, some toxic plants even have medicinal uses. Thevetin from the yellow oleander can be used as a remedy for heart disease; the roots of the oleander yield a substance used to treat skin diseases; and extracts of the leaves, roots and flowers of the allamanda have shown to be effective in treating leukaemia in mice and carcinoma of the nasal cavity in humans. Using these plants' substances unsupervised, however, must never be attempted.
Dieffenbachia, a popular indoor as well as garden plant noted for its patterned leaves, also has its uses apart from beautifying homes and gardens. In a Nasa study conducted to find ways to clean the air in space stations, the dieffenbachia was found to be among plants capable of removing toxins and pollutants.
Even the multi-coloured plumeria, which was discussed in this column two weeks ago, and the Christmas iconEuphorbia pulcherrima, or poinsettia, can cause irritation of the skin with their milky sap. The cassava, which is a staple food in many developing countries and cooked into many kinds of desserts _ often used as an animal feed in Thailand _ can be poisonous when raw, but perfectly safe to eat when cooked.
Poisonous plants can be harmful, and in some cases even deadly when ingested. Instead of being scared of these plants, all we have to do after handling them is wash our hands, and not be in the habit of chewing on plant leaves and stems unless we know for sure that they are edible. Train your children to do the same, and don't panic if you accidentally get irritation of the eyes or skin; it can be easily remedied by washing the affected area with running water. If symptoms do persist, however, make sure to see a doctor.
Like the plumeria, all poisonous flowering plants require full sun and thrive best in well-drained, loamy soil mixed with compost and animal manure. If planting them in the ground, dig a hole deep and wide enough to accommodate the plant's root ball, plus an allowance of 20cm all around it, to facilitate the growth and spread of roots. Water regularly until the plants are well established, after which they can be watered only as needed.
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NO MELLOW YELLOW: All parts of the yellow oleander and its cousin, the oleander, are highly poisonous.
