I was asked to speak with you today, among other reasons, because I'm an amateur horticulturist with an amateur’s acquaintance with toxic plants. Clearly, from your point of view, this has some disadvantages. What you may not realize is that my amateur status may be all that is needed to keep you out of the ranks of a new human subspecies which I have named Homo sapiens hysterics, and which I suggest is gradually, supplanting Homo sapiens. Homo hysterics lives in a world of perpetual and imminent danger, and is prone to damage more from the violence of his efforts to avoid danger than from the threat itself. A few weeks ago in this very city, at a large public gathering on the Parkway, 59 people were treated for minor injuries when the crowd panicked at the sound of a few firecrackers. Not too many years ago I think . . . . I hope . . . we'd have taken this kind of thing in stride. So, that I propose today is a non-hysterical approach to the problems of toxic plants in zoological gardens.
Frankly, I'm not sure there is a problem. Our host has stated that he has no knowledge of any zoo deaths from this cause. Well, then? How do we provide answers if there are no questions? Faced with this dilemma, to prepare for today I set out to locate the questions? The list is short. I came up with three. Perhaps some of you could lengthen it.
- Are there plants which have been known to cause death of zoo animals?
- Is the intrusion of local flora which may damage human visitors to the zoo such as poison ivy, thorny bushes, etc. a problem for zoo managers?
- Occasionally domestic animals succumb to plants in pastures or silage (water hemlock, cockleburr, Jimson weed). Must the zoo manager be alert to these?
We'll talk more about these problems, if they are problems, but first let's go back to the emotional approach. The typical book which deals with poisonous plants can be frightening. It prints lists whose length is astounding and which include names whose presence is astounding. Consider Walter Conrad Muenscher's POISONOUS PLANTS OF THE UNITED STATES, with a list of 99 plants that cause dermatitis. . The list includes the young stems of asparagus, the flowers of Catalpa speciosa, the leaves of the Wild Carrot, English Ivy, primroses, lily-of-the-valley and Viper's Bugloss, and the rhizomes of Iris species. Surely we humans are surrounded with dangers there are even reports of "a number of cases of contact dermatitis. Among farmers and others handling large quantities of celery" I However, be of good cheer. Muenscher says and I quote: "Most poisonous plants... are harmful only when they are eaten. Relatively few plants produce poisoning by contact'. In a sense 99 isn't all that many (even if it does include such common species as Ailanthus, Burdock, Jack-in-the-Pulpit, Box, Daphne, Larkspur and Ginkgo) seeing that there are at least 30,000 from which to choose.
All this may be interesting but of no great significance for zoos since dermatitis from contact poisons isn't significant for animals other than humans. As always, there are exceptions. Some plants contain chemicals called photosensitizers which can cause animals to develop a great sensitivity to light. Now the animals are subject to sunburn, which can be serious for albino or partly white individuals. Even death may follow, from starvation, because the animals' mouths become so badly burn that they can' t eat. St. Johnswort (Hypericum perforatum and H. crispum), Ladies Thumb (Polygonum) and Alsike Clover all cause photosensitization. I looked this up in a couple of books with titles like A VETERINARY GUIDE FOR ANIMAL OWNERS. Photosensitization was not mentioned.-In fact, there was no mention of any disease brought about by toxic plants. Obviously, there is no crying need for preventive work here.
I do not mean to deny that there are toxic plants in the world. The legion of sufferers from exposure to Rhus radicans and others of its genus would surely raise a brow. Also, in a recent year, of 161,500 and some cases of possible ingestion of poisons which were reported to the National Clearing House for Poison Control Centers, over 11,000 involved plants. Since most cases are probably not reported it is difficult to come by a true total. Some authorities like to talk about 50,000 to 100,000 a year. True to the principles of Homo hysterics, most of these so-called "cases" weren't actually poisoned. To be counted, it was only necessary for a person to swallow a plant or plant part that was suspected of being poisonous. For instance, 442 of these cases involved Pyracantha berries, which taste terrible but aren't dangerous.
Nevertheless, there are poisonous plants which can and do have serious if not fatal effects. A recent listing of the top ten gives Philodendron, Yew, Pyracantha, Bittersweet, Marijuana, Holly, Poinsettia, Dieffenbachia, Elderberry and Oleander. These aren't necessarily the most poisonous plants around, but they are among the most accessible. Four are house plants, reflecting the recent national preoccupation with potted and hanging plants. Holly and Bittersweet often find their way into our homes. Marijuana . . . well, what can I say? Yew and Pyracantha are cliché plants in the suburbs, as I gather is Oleander in the warmer parts of the country.
PHILODENDRON, with calcium oxalate in the leaves, causes burning of the mouth, vomiting and diarrhea. I first met calcium oxalate on a college botany class field trip. The instructor, an old-timer, invariably served slivers of JACK-IN-THE-PULPIT corms to unsuspecting students, whoe burning mouths were instructive in an unpleasant way. I suppose if you did this in 1980 the students would sue the university, so I leap to assert that I do not endorse this instructional technique. Incidentally, the starchy corms of JACK-IN-THE-PULPIT were boiled and eaten by Native Americans. YEWS have fleshy red berries about the size of a pea, open at one end showing the single hard seed inside. The seeds of most species are poisonous, capable of causing vomiting, diarrhea, dilated pupils, weakness and convulsions. Sometimes the foliage is poisonous when eaten by livestock. In his book, POISON PLANTS, Alan Eshleman says "Very few gymnosperms are poisonous, but the YEW makes up for this be being very poisonous. All parts . . . contain the poisonous alkalois taxine. Animals are sometimes killed from eating the bark, leaves or seeds. People are most often poisoned by the fruit of the YEW tree. (I contend this phraseology is typical Homo hysterics style. Most or all of us have grown up with large populations of yews and have lived to be here today.) If children eat enough of these berries they can get very sick, but luckily the fruit is the least poisonous part of the plant, so death from yew poisoning is very rare." PYRACANTHA was mentioned earlier, not too seriously, BITTERSWEET, or WOODY NIGHTSHADE, also known as BITTER NIGHTSHADE and DEADLY NIGHTSHADE, is a climbing vine from Europe which has become naturalized in North America. It has attractive purple flowers and brilliant scarlet berries. Both leaves, berries and shoots are very poisonous when eaten, so the plant should not be near children or grazing animals. The related COMMON NIGHTSHADE, Solanum nigrum, with black-purple berries is also an enemy. MARIJUANA leaves and flowers are said to be poisonous, overdoses producing nausea, poor coordination and rarely, coma. Various species of ILEX or HOLLY have berries which may cause vomiting and diarrhea. Eshleman says "probably more than twenty" berries, need to be ingested, which would seem to indicate that nineteen are okay. POINSETTIA leaves and stems can cause stomach upset, but this plant's reputation is probably far more fierce than it deserves. DIFFENBACHIA, DUMBCANE, has a highly acrid sap that irritates the mucus membranes so much that speech is difficult or impossible for several days “After it is- eaten. It has been said the Dumbcane used to be given to slaves as punishment. Elderberry, Sambucus canadensis, grows wild over much of the U.S. Fresh leaves, flowers, bark, young buds and roots contain a bitter alkaloid, producing I prussic acid and causing fatal results if eaten by cattle and sheep. Poisoning of children has been ascribed to chewing or sucking the bark. However, jellies, preserves "- and wines are made from the small, blue-black berries which ripen in the late summer. Finally OLEANDER, common in the south, California and Hawaii has leaves which are highly toxic both in green and dry condition; all parts of the plant are toxic. It can cause vomiting, abdominal pain, dizziness, slow and irregular heartbeat, dilation of pupils, bloody diarrhea and respiratory paralysis. Phew:
The poisonous properties of a plant may be due to a single chemical, several similar compounds, or to substances with very different chemical properties. Most common are alkaloids, which are found in the lily, poppy, buttercup and potato families and in certain legumes. Correctly used, alkaloids of some plants have medicinal value, such as atropine, caffeine, cocaine, morphine, nicotine, quinine, strychnine and the extract of curare. Other poisonous substances are glucosides of Prunus, Sorghum and flax; resinoids in heaths; phytotoxins of Black Locust and the Castor Bean. Oxalic acid is the poison in rhubarb leaves. It is present in many other plants but seldom in quantities sufficient to cause poisoning.
Most cases of plant poisoning in humans and animals (setting aside skin irritants) are caused when the toxic principle is eaten. Clearly, then, it must be present it must be there in sufficient quantities and it must be palatable. This last requirement rules out the vast majority of plant poisons, for relatively few plants taste good. Most people confuse the terms "inedible" and "poisonous", assuming that anything inedible is poisonous. Now I am an inveterate taster (and smeller) of plant parts as an aid in identification and probably have indulged in a substantial number of those mentioned so far. Most of them taste awful, or are relatively tasteless. Few incite one toward gluttony.
There is an article in the April 1977 issue of Horticulture by a pediatrician at the Kaiser/Permanente Medical Center in Fontana, CA. Dr. Guy Hartman describes The Sinister Garden, a collection of poisonous plants growing just outside the Pediatric Clinic. Some visitors who see azaleas, poinsettias and iris officially labeled poisonous are determined to rush home and redesign their gardens. Don't, says he. "Replant your azaleas. Rescue the poinsettias, and defend the iris. I will personally guarantee that none of them will kill any of your progeny A sound thinker, This: To quote further: " . . .it would require 1/4 to 1/2 pound of azalea vegetation to seriously poison a 2 5 l b child . . . the poinsettia is not entirely harmless (but) the myth of its fatal toxicity has been thoroughly debunked by recent research; and I cannot imagine and toddler digging up the iris rhizome for an afternoon snack . . . The Sinister Garden was planted not to terrify concerned parents... but to educate the public to potential dangers lurking unsuspected in their backyards." This article says that of the 700-plus poisonous plants in the United States probably only the castor bean and oleander ought to be kept away from young children.
A reasonable question along about here is. Does any of this have anything to do with zoo animals? Of course, you know more about this than I do. However, as in humans the frequency of poisoning is often a result of a lack of more palatable food, a condition not likely to confront captive animals in the modern zoo. Of course, some poisonous plant may be present in hay and coarse feeds, and a few cause trouble only or primarily when fed in ground feeds. A noted authority, Dr. John M. Kingsbury, writes -.1 of toxic effects occurring in animals after ingestion of 1-11% to 5% of their body weight, or after they have grazed on a certain plant exclusively for a number of days or weeks. Again, these are unlikely scenarios for zoo animals. To sum up this point here is a quote from Muenscher: "Most cases of stock poisoning occur either in the early spring when the grass is still short...or in late summer when the grass is dried up . . . Under such conditions of scarcity of forage, animals are frequently forced to eat poisonous plants which would otherwise be left untouched." So we are given to understand that undesirable plants will not be consumed if an adequate supply of good feed is provided.
Are you beginning to accept that this is, or could be, or ought to be a very dangerous world? Azaleas, caladiums, delphiniums, flax, tobacco and jimson weed carry toxins in all of their parts. Agave, avocado, ranunculus and foxglove concentrate them in their leaves. Holly, ivy, privet and mistletoe offer us poisonous berries. Elder, cherries, apricots, peaches, plums, eggplants and tomatoes produce edible fruits on plants otherwise hostile, and with many of these the seeds inside the edible fruits are dangerous. Pokeweed and acorns can be in your diet, but beware of them improperly prepared. Get your medicinals from foxglove and lobelia, but for heaven's sake don't eat them, enjoy the leaf stalk of rhubarb; beware of the leaf blade. Be sure to swallow the seeds of cherries, castor beans the rosary pea intact so the seed coat can protect you from the toxic substances inside.
With all these hazards can animal life as we know it survive? Well . . . yes. Of course. Our own life experiences tell us so. The problem is manageable. In fact there is very little we need do about it.
The Philadelphia Zoo has performed autopsies on all of its casualties for more than 65 years and has no record of a death from plant toxins. To my knowledge no zoo has been sued for exposing visitors to poisonous plants. Finally, hay or feeds which cause problems are easily replaced.
We've answered our three questions. What's left? I contend there is a good point to be made for extending the educational functions of the zoo in this area. Why not your own Sinister Garden? Why not try to get across the truth about poison ivy, yew, and dieffenbachia? The crowds that come to see captive animals make a beautiful captive audience. Why not inject them with a bit of the horticultural along with the zoological? With more than just name tags? Arboretums will never compete with zoos as crowd gatherers, so I think there is a tremendous opportunity for zoo-Hort folks to perform an additional public service. We should be introducing toxic species in a controlled way, not eradicating them. Planting is what you are all about. The real challenge is to eradicate- not toxic plants - but the Homo hysterics subspecies along with all those fears which a little reason and knowledge can show to be unnecessary.
* Paper given at the First AZH Conference by Val Udell, Director of Product Development, D.C.A. - Educational Products, Warminster, Pa., Subsidiary D.C.A. Inc.