JARS v64n2 - Apples Can Kill You - Rhododendrons Can Too
Apples Can Kill You - Rhododendrons Can Too
M. J. Harvey
Victoria, British Columbia
Canada
Modified from the September 2009 Victoria Rhododendron Society NewsletterI have a confession to make: when I was at school I just loved chemistry, still do, some 64 years later. Early influences stay with you. So it was with delight that I seized on an attractive book that came into the Victoria Horticultural Society library a few years ago. Since most people are unlikely to read it I thought a slightly extended review might be in order.
The book is Poisonous Plants by Frohne and Pfander (2005), two Germans working in the emergency department at Freiburg Hospital. The beauty of the book is the ease of use. It is laid out alphabetically by plant family and each family has one or more large, clear, photographs of a flowering shoot. There is no problem looking up a particular plant; that part is easy.
Where the book may give indigestion is in its use of technical terms. You soon hit words like fumanocoumarins (more later) and indeed the book is a "handbook for Doctors, Pharmacists, Toxicologists, and Veterinarians," so the Germanic obsession with detail can be excused. But gardeners will find that reading around the technical terms can be quite rewarding. Let me give a few examples.
In the classical writings there is an ancient tradition that the honey which bees have made from Rhododendron flowers is poisonous. Reports by Pliny and Xenophon detail sickness in soldiers invading what is now northeastern Turkey following their consumption of local honey. Subsequently their army was defeated. Is this myth? Is Turkish honey still poisonous?
Honey from Turkey can still be a problem since the simultaneous flowering of many hectares of the fragrant, yellow azalea R. luteum can result in bees collecting almost pure Rhododendron nectar.
Toxic effects include drooling, dizziness, vomiting and unconsciousness. After receiving many names, the compounds responsible are now called grayanotoxins. Molecules of these attach to channels in cell membranes allowing sodium ions to leak out and calcium ions in. This has nerve and cardiac consequences, possibly fatal.
The presence of toxins in nectar is variable in the species of Rhododendron , being present in some, absent in others. Currently, the American Rhododendron Society has given a grant to a researcher in the University of Newcastle upon Tyne to investigate the distribution of grayanotoxins and any connections this might have to pollinators predicted on the basis of rhododendron floral traits (see #08-4, JARS 63 (Winter 2008)).
Readers will be delighted to hear that the other genera in Ericaceae, particularly Vaccinium , are toxin free, and thus cranberries and blueberries may be indulged in freely. However, personally I would not touch tea made from the leaves of Labrador tea. Its old name was Ledum , but it is now transferred to Rhododendron , and something in those leaves has to stop hungry moose from touching it.
Another example is the opium poppy Papaver somniferum . This produces opium, a complex mixture of maybe forty or so alkaloids. Opium is a "schedule 1" drug and the cultivation of the poppy and the production of opium is prohibited. The problem here is that most gardens in most cities in the temperate world have buried seeds of the opium poppy, mostly as the double garden variety. You dig the soil, light strikes the seed, they grow; you are a criminal. I was once assured that the police do not patrol gardens looking for the odd ornamental poppy - but that was before 9/11.
Poppy seeds contain negligible amounts of alkaloids, so poppy seed cake will not give you a high. On the other hand the test for opioids is so sensitive that they can be detected for a few days after a person has eaten only a couple of poppy seed bagels. This could cause problems for some!
So what do we grow that is really poisonous? High on the list are monkshood ( Aconitum ), castor oil plant ( Ricinus ), Colchicum , Daphne and the spurges ( Euphorbia ). The book discusses very sensibly whether we should rip out all dangerous plants, and concludes that this is not necessary. Most poisonous plants are not dangerous because they taste really bad. After all, these substances are animal repellents variously aimed at different levels of the animal kingdom from deer to slugs to aphids and weevils inside seeds. There are some particular dangers; for example, three Daphne mezereum berries could kill a toddler and when kids are young - the terrible twos - everything goes into the mouth, and the red berries of Daphne look pretty. We have solved this problem since children are now monitored 24/7. They are shepherded from air-conditioned home to air-conditioned mall to ultra-safe playgrounds with no grass or trees. Richard Louv's (2008) Last Child in the Woods has termed this the "nature deficit." When we were trying to sell our Sooke, BC, acreage, I was showing off the orchard, picking apples to hand to open-house visitors and was shocked to find that one girl had no idea that apples grew on trees.
The most common cases of poisoning among gardeners involve getting sap of euphorbias in the eye. Extremely small traces cause severe eye inflammation. Gardeners who prune dead flower heads off the large euphorbs, especially E. carassias , get abundant amounts of the milky sap on their hands and should be acutely conscious to avoid touching the face. Do not merely wash the hands afterward but scrub them. I have myself been affected and it is nasty.
I love it when people tell me "I never use chemicals." Everything is made of chemicals and the natural world has more chemicals, many very nasty, than all the hundreds of thousands that man has made. Certain crops are cultivated for their unusual chemical content: we love caffeine in coffee, capsaicin in chilies and allyl isothiocyanate in mustard.
Sometimes we get caught as with the previously mentioned furanocoumarins in grapefruit. This class of substances slows down a system in the liver that breaks down and eliminates some groups of chemicals. One example is digoxin (from foxglove, Digitalis ) taken for certain heart problems. Eating grapefruit while taking this drug may cause it to accumulate in the bloodstream, causing an overdose. Ask your pharmacist about possible compromised medications.
It has become popular to mistrust science. People want to use only "natural" cures for complaints, rather than the "synthetic" drugs that scientists are "foisting" on them. This is a complete misreading of the situation. While you can trust most herbalists and naturopaths to prescribe harmless remedies, going out yourself with limited knowledge and picking your own herbs can result in disaster. Plants can be anything but harmless.
So, can apples kill you? Yes. One person managed it. He loved chewing on the crunchy seeds, so having saved up three quarters of a cupful, he decided to chew them one evening and was found dead the next day. Why? Cyanide poisoning! Apples are a complex fruit; I could give a wholelecture on their structure and chemistry. From the apple's point of view, the ultimate product is the seed - all the rest is marketing. So the seeds are protected by a tough core, unattractive color and, inside, a substance which releases cyanide when eaten.
Should we ban apples and rhododendrons because they can be deadly? No. My purpose in writing this is not to inculcate fear but to impart knowledge about subjects you may not have thought about. With knowledge comes confidence. Enjoy an apple, a few seeds swallowed will not harm you and your liver protects you, but be careful of honey from Turkey.
References
Frohne, D., and H.J. Pfander. 2005. Poisonous Plants, a handbook for doctors, pharmacists, toxicologists, biologists and veterinarians . Timber Press, Portland, OR. (Translated from the German fifth edition): 469 pp.
Louv, R. 2008. Last Child In the Woods: Saving Our Children from Nature-Deficit Disorder . Algonquin Books of Chapel Hill, NC: 348 pp.
Dr. Joe Harvey is a member of the Victoria ARS Society.
