Toxic plants in Prairie Gardens.
Compared to animals, plants are biochemically advanced. Besides producing all of the molecules required for primary metabolism (respiration, photosynthesis, and protein, lipid and nucleic acid synthesis and breakdown), plants have developed an incredible array of convoluted metabolic pathways to produce thousands of secondary compounds that play a role in defence, storage and other functions (some common examples are listed in Table 1, next page). These substances may taste or smell bad, or better still, many provide a permanent solution by being toxic. Some, such as precocenes, which prevent juvenile insects from moulting into reproductive adults, mimic animal hormones and thus control pest populations. Other chemicals deter disease invaders (antimicrobial and antifungal agents), confer plant immunity (phytoalexins), discourage other plants from encroaching on the plant's personal space (allelopathic compounds), or are simply indigestible and, therefore, waste the herbivore's time and energy (e.g., inulin instead of starch in dahlia tubers). Plants have experimented with molecular structures in the most creative and ingenious ways, even devising ways to incorporate environmental toxins such as selenium and fluorine into organic compounds that are toxic to animals but not to the plants themselves.
To deal with different kinds of herbivores and feeding preferences, many plants have diversified their chemical arsenals by producing more than one type of toxin at the same time. The target varies. Compounds can be nerve, heart or liver poisons, may disable kidneys, may disrupt blood clotting or cause anemia, interfere with iodine metabolism, cause gastrointestinal rebellion, block key respiratory enzymes, act as carcinogens (e.g., furanocoumarins in bergamot oil, which has been banned from lotions by the European Union since 1995), or cause photosensitization when the animal is exposed to sunlight. In other cases, simple contact with the plant may produce severe allergic reactions and skin lesions. Every animal metabolic pathway has a plant compound that affects it. Many of these substances, accordingly, provide us with useful drugs and natural pest control products.
In our own role as herbivores, it is therefore important for us to be aware of potentially harmful plants, especially in our gardens. Toxins are almost impossible to avoid in our foods, and our bodies are able to handle small amounts of substances such as cyanide compounds in almonds or oxalic acid in spinach without visible ill-effect. However, injudicious consumption of large quantities can very quickly lead to toxicity. The threshold is a very fine line and depends on the individuals and their age, state of health, and sometimes gender, genetic make-up of both consumer and plant, and many other factors which are still unknown.
We also need to be aware that many medicinal plants used in herbal therapy may be toxic if: used in unsuitable dosages; stored or prepared incorrectly; the inappropriate plant part (or inappropriate stage of growth) is used; the plant has been cultivated under questionable conditions (e.g., heavy metals, nitrates, pesticides); or if it is used in combinations with certain other ingredients (drugs or food) which may interact. Of particular concern are herbal weight-loss preparations (e.g., Lamiaceae, some Euphorbiaceae), which may cause permanent liver damage even when immediate effects might not be apparent. Whether you are dosing yourself or you are using purchased, ready-made preparations, you must be cautious because in numerous cases, plants have been incorrectly identified or adulterated by suppliers. It is best to stay away from more exotic ethnic imports.
For some species, only certain parts may be toxic, as for example potatoes, tomatoes or asparagus. Or just a part of a plant may be toxic: in rhubarb, only the green part of the leaf is toxic due to soluble oxalates but the stalk contains much lower concentrations. Other plants may be toxic only at certain stages of their life cycle--for example, lettuce becomes toxic once it has bolted and started to flower, causing an illness known as lettuce opium poisoning (which has nothing to do with true opium, so don't get any ideas). The bitter compounds that develop at this stage give us some warning that it should not be eaten. Yet others may become toxic if grown under certain conditions. Good examples are spinach and chard, which should never be grown in soil richly fertilized with nitrogen, as they may accumulate enough toxic nitrates in the leaves to cause an illness called methemoglobinemia (in people) or nitrate toxicosis (in livestock). Some canned spinach has had to be recalled for this reason. Other reported nitrate accumulators include celery, beet, turnip, broccoli, sweet potato, lettuce, radish, cucumber, squash, sunflower and even corn. So it is wise never to overdo the chemical fertilizer or manure. Nitrate absorption is aggravated even more in plants that have been exposed to herbicides like 2,4-D or MCPA. Thus nitrate toxicosis in cattle can become a big problem in pastures that have been sprayed, where there is already a high amount of nitrogen in the soil.
Some plants may produce toxins depending on the genetic strain and environmental conditions. Prussic acid (cyanide) in lima beans may reach 0.3% in some strains from South America. Although Canada prohibits importation of lima beans with more than 0.02% prussic acid, small quantities of heritage seeds may still find their way into Canadian gardens undetected. Mediterranean peoples are especially susceptible to illness from fava bean consumption (a type of anemia called favism) because of a particular X-linked human gene.
Beet leaves may contain more oxalates than rhubarb leaves in some conditions (levels of 12% by weight have been reported), and it is impossible to predict how much is present in the plants from your particular garden at any given time, as toxin levels depend on variety of beet, age of the leaves, soil and light conditions, stress and so on. Irreversible silent liver and kidney damage are the rewards of frequent consumption, and may lead to fatal uremic shock (many traditional recipes still include beet leaves). Similarly, oxalic acid in sorrel (Rumex crispus) has resulted in human death after ingestion of 500 grams of leaves prepared as sorrel soup, and this plant is frequently responsible for death of sheep both here on the prairies and in Europe.
Many other plants that were used indiscriminately by our grandmothers (grandfathers hardly ever seemed to cook) have now been redlined as more information comes to light. Raw kidney bean seeds contain toxic lectins which fortunately are destroyed on cooking. These proteins cause pathological changes in the intestinal lining and inflammation of heart muscle; numerous cases of poisoning have been recorded in children and adults from batches of undercooked beans. Similarly, there are many recipes for green tomatoes: these should be consumed with caution and in moderation as they contain alkaloids with neurological and gastrointestinal effects designed to deter mammals from eating the fruit before the seeds are ready to be dispersed.
Plants that are poisonous to people are also often poisonous to livestock and other animals, but not necessarily vice versa. NEVER assume that because you see an animal or bird eating something, that it is safe for humans to eat. Squirrels, for example, often die from plant or mushroom poisoning in the wild. Contrary to popular myth, they DON'T know any better than we do. As any gardener knows, deer are often seen to eat toxic species (such as delphinium), even when food isn't especially scarce. Birds can safely eat many kinds of berries that are toxic for mammals, such as cotoneaster and yew. Bees can collect nectar from poisonous plants like rhododendron and azalea, which, although harmless for bees, yields poisonous honey for us. Sometimes however, plants which may seem harmless for us, such as onions, may prove fatal for dogs, cats and livestock, causing a type of lethal anemia. Similarly limonene in citrus oils is repellent and toxic to cats and many other animals; hence its use in animal deterrent products.
A good rule is don't eat or taste any plant with which you are unfamiliar. Also, supervise children in the garden and train them from an early age never to put leaves, berries or even flowers into their mouths. For instance, children have been poisoned by sucking nectar out of angel's trumpet flowers (Datura). Wash your hands after handling poisonous plants, or better still, wear gloves, and don't rub your eyes. Don't feed the discards from your garden to cattle, horses or pigs. It is amazing how many animals continue to die needlessly from being allowed to eat tomato and potato stalks, leafy beet tops, bolted lettuce and rhubarb leaves tossed "over the garden fence."
Don't use flowers and leaves from plants of which you are not sure to decorate food. Some lavishly illustrated cookbooks show food decked with poisonous flowers--while this makes for a prettier picture, it is not so pretty if you try to copy the picture and picture yourself afterwards in the emergency ward. Flowers which are generally thought to be edible include rose, nasturtium, giant hyssop (Agastache faeniculum), common hyssop (Hyssopus officinalis), honeysuckle (Lonicera caprifolium), bergamot, fennel, basil, chive, summer savory, marjoram, hop, various mint species, pot marigold, pinks (Dianthus), hollyhock, stocks (Matthiola), angelica, squash, dandelion, sunflower petals. Note that allergic reactions and unpredictable interactions with other food ingredients may affect certain individuals, therefore always use in moderation. Persons with diabetes, or liver or kidney ailments are especially susceptible to adverse reactions. Crystallized violets, a Victorian favorite, are not commonly seen now, owing to their tendency to cause diarrhea and cramps.
Table 2 (next page) lists some of the toxic plants that are commonly found in prairie gardens. For many plants, some parts have been shown to be poisonous, but there may be insufficient data regarding the other parts. So if a species part is already listed, don't assume that the other parts are safe, unless they have been proven. This is how these data are collected--from somebody's unfortunate experience. You probably don't want to become another testimonial in this hall of fame!
Blackwell, W.H. 1990. Poisonous and Medicinal Plants. Prentice Hall, Englewood Cliffs, NJ.
Bruneton, J. 1999. Toxic Plants Dangerous to Humans and Animals. Lavoisier Publishing, Paris.
Emboden, W. 1979. Narcotic Plants. Collier Books, New York, NY.
Hole, L. 2000. Herbs & Edible Flowers. Hole's, St. Albert, AB.
Kingsbury, J.M. 1965. Deadly Harvest. Holt, Rinehart and Winston, New York, NY.
Leggatt, J. 1987. Cooking with Flowers. Fawcett Columbine, New York, NY.
Newdick, J. & M. Lawrence. 1991. Flowers as Food. Crescent Books, New York, NY.
Ott, J. 1976. Hallucinogenic Plants of North America. Wingbow Press, Berkeley, CA.
Stephens, H.A. 1984. Poisonous Plants of the Central United States. University of Kansas Press, Lawrence, KS.
Tampion, J. 1977. Dangerous Plants. David & Charles Publishers, Vancouver, BC.
Warning: The following articles deal with more toxic plants. Many are highly poisonous and are not recommended for gardens used by children or pets. Always wash your hands thoroughly after handling any toxic plant, and it is recommended that gloves be worn at all times. Ingesting such plants can be deadly. Ingestion is not recommended.
Dr. Eva Pip is a Full Professor at the University of Winnipeg. She lives in the Cloverleaf area in Eastern Manitoba. Eva has taught courses in plant anatomy, physiology and taxonomy for over 25 years.
Table 1: Some Examples of Common Plant Secondary Com wounds Compound Where Found Alkaloids In many flowering plant families, >10,000 identified so far Unusual amines In many flowering plant families, often flowers Cyanogenic At least 2650 species in 130 glycosides families, often seeds and young leaves Cardiac Some Apocynaceae, Asclepiadaceae, glycosides Scrophulariaceae, Brassicaceae, Crassulaceae and others Glucosinolates Brassicaceae and other families in order Ca aridales Coumarins A iaceae, Rutaceae and others Unusual Convolvulaceae, Sterculiaceae, castor fatty acids bean (ricinoleic acid) Phenols Universal Monoterpenes In >50 families with essential oils, localized in specialized cells and ducts Diterpenes Many latex and resin producing secies Limonoids Turaceae, Meliaceae, Simaroubaceae Cucurbitacins Cucurbitaceae and some others Sesquiterpene Asteraceae, Lauraceae and others lactones Tannins Widespread, especially in woody species Saponins Sporadic Polyacetylenes Asteraceae, Umbelliferae Unusual Leguminosae dipeptides Unusual Leguminosae and orb ers proteins Selenium Asteraceae, Leguminosae, compounds Cheno odiaceae, Scro hulariaceae Fluorine Leguminosae, Rubiaceae, compounds Dichapetalaceae Compound Qualities Alkaloids Bitter and/or toxic, many interfere with animal neurotransmitters Unusual amines Unpleasant taste, some hallucinoraenic Cyanogenic Cyanide released when glycosides compounds react with digestive enzymes Cardiac Increase strength of cardiac glycosides muscle contractions, decrease heart rate Glucosinolates Unpleasant taste Coumarins Cause hemorrhtye Unusual Interfere with lipid metabolism fatty acids Phenols Antimicrobial Monoterpenes Volatile with strong odour, may intoxicate Diterpenes Astringent taste, some toxic Limonoids Unpleasant taste Cucurbitacins Unpleasant taste, some toxic Sesquiterpene Allergens, neurolo?ical toxins lactones Tannins Inhibit digestion by binding to proteins; some toxic Saponins Detergents; stimulate intestinal contractions and hemolyze blood cells Polyacetylenes Some toxic Unusual Lathyrogens cause paralysis, dipeptides premature in (lath rism) Unusual Allergens, hematemesis, proteins fainting, blood clots Selenium Appetite loss, reproductive compounds problems Fluorine Toxic respiratory enzyme compounds inhibitors Table 2: A Partial List of Common Toxic Prairie Garden Plants This list does not include houseplants, native species or fungi. Where only genera are listed, all species should be considered suspect until more data prove otherwise. See end of table for notes. Name Common Name Aconitum * Monkshood Acorus calamus Sweet Flag Aerculus Buckeye Agrostemma Ornamental Corn Cockle Allium giganteum Giant or Tibetan Onion Amaranthus Amaranth Amaryllis Amaryllis Anchusa Summer Forget-Me-Not Anemone Anemone Antirrhinum Snapdragon Aquilegia Columbine * Arisaema triphyllum Jack in the Pulpit Artemisia * Silver Artemisia, Wormwood Asdepias Monarch Butterfly Milkweed Asparagus Asparagus Aster Aster Azalea Azalea Baptisia False Indigo Begonia Begonia Beta vulgaris *** Beets Borago officinalis ** Borage Browallia Browallia, Blue 'Violet' Brugmansia * Brugmansia, Trumpet Flower Caladium Caladium, Angel Wins Caltha palustris Marsh Marigold Clematis Clematis Colocasia Elephant's Ear Convallaria majalis Lily of the Valley Convolvulus Morning Glory Corydalis Fumatory Cotoneaster Cotoneaster Craetegus Hawthorn Cyclamen * Cyclamen Cynoglossum Chinese Forget-Me-Not Datura * Angel's Trumpet Daucus Carrot, Queen Anne's Lace Delphinium Larkspur (annual + perennial) Dicentra * Bleeding Heart Dictamnus * Gas Plant, Fraxinella Digitalis * Foxglove Echinops Globe Thistle Escholtzia California Poppy Eupatorium Joe Pye Weed Festuca arundinacea Tall Fescue Fritillaria Crown Imperial, Fritillary Galanthus Snowdrops Gladiolus Gladiolus Gloriosa superba * Gloriosa Lily Vine Hedera helix English Ivy Helenium Helen's Daisy, Sneezeweed Heliotropium * Heliotrope Hyacinthus Hyacinth Hydrangea Hydrangea Hypericume perforatum St. John's Wort Impatiens Impatiens Ipomoea Morning Glory Iris Iris Lactuca sativa Lettuce Lathyrus Sweet Pea (annual + perennial) Ligularia Groundsel Lilium Garden Lilies Linum Flax (scarlet + perennial) Lobelia Lobelia Lupinus * Lupine Lycopersicon Tomato esculentum Malus * Apple Menispermum Moonseed canadense Mirabilis jalapa Four O'Clock Monarda Bergamot Myosotis Forget-Me-Not Nicotiana * Flowering Tobacco Narcissus Daffodils, Narcissus Nierembergia Nierember is Nymphaea, Nuphar Water Lily Ornithogallum Star of Bethlehem Paeonia Peony lactiflora Papaver * Poppies Parthenocissus Virginia Creeper virginianus Penstemon Beard's tongue Petunia Petunia Phaseolus lunatus Broad or Lima Bean, Fava Bean Phaseolur vulgaris Kidney Bean Philadelphut * Mock Orange Polygonatum Solomon's Seal Portulaca Portulaca Prunus * Plum, Cherry, Apricot Pteridium aquilinum Bracken Fern Ranunculus Buttercup Rheum * Rhubarb Ricinus * Castor Bean Rumex * Sorrel, Yellow Dock Salvia reflexa Ornamental (annual) Salvia Sambucus Elderberry Sanguinaria Bloodroot canadensis Saponaria Soapwort Scilla * Squill Solanum * Potato, Nightshade Solidago Goldenrod Sorbus Mountain Ash Symphytum officinale Comfrey Tanacetum Tansy Tulipa Tulip Vinca Periwinkle Zantedetchia Angel Wings, Caladium Scientific Name Poisonous parts Aconitum * All parts Acorus calamus Root Aerculus All pparts Agrostemma Leaves Allium giganteum All parts Amaranthus All parts Amaryllis Bulb Anchusa All parts Anemone All parts Antirrhinum Leaves Aquilegia All parts Arisaema triphyllum All parts Artemisia * All parts Asdepias All parts Asparagus Berries, mature leaves Aster All parts Azalea All parts Baptisia All parts Begonia All Paris Beta vulgaris *** Leaves only Borago officinalis ** Leaves, flowers Browallia All parts Brugmansia * All parts Caladium All parts Caltha palustris Leaves Clematis Leaves Colocasia All parts Convallaria majalis All parts Convolvulus Seeds Corydalis All parts Cotoneaster Berries Craetegus Fruits Cyclamen * Roots Cynoglossum All parts Datura * All parts Daucus Leaves Delphinium All parts, young foliagemost toxic Dicentra * All parts Dictamnus * All parts Digitalis * All parts Echinops Leaves Escholtzia Seeds Eupatorium All parts Festuca arundinacea Leaves Fritillaria All parts Galanthus Bulbs Gladiolus Corms (bulbs) Gloriosa superba * All parts Hedera helix Leaves Helenium All parts Heliotropium * All parts Hyacinthus All parts Hydrangea Leaves Hypericume perforatum Leaves Impatiens Leaves Ipomoea Seeds Iris All parts Lactuca sativa Leaves of bolted plants Lathyrus Seeds Ligularia All parts Lilium All parts Linum Leaves Lobelia All parts Lupinus * All parts Lycopersicon All green parts esculentum Malus * Bark, leaves, seeds Menispermum Leaves, fruits canadense Mirabilis jalapa Roots, seeds Monarda Leaves Myosotis All parts Nicotiana * All green parts Narcissus All parts Nierembergia All parts Nymphaea, Nuphar All parts Ornithogallum All parts Paeonia Seeds lactiflora Papaver * Leaves, pods Parthenocissus Berries and seeds virginianus Penstemon All parts Petunia All parts Phaseolus lunatus All parts (If grown in nitrogen fertilized conditions) Phaseolur vulgaris RAW seeds only Philadelphut * Seeds Polygonatum Berries Portulaca Leaves Prunus * Leaves, bark, seeds inside pits Pteridium aquilinum All parts Ranunculus All parts Rheum * All green parts Ricinus * All parts Rumex * Leaves Salvia reflexa Leaves Sambucus Leaves, bark Sanguinaria Roots canadensis Saponaria Seeds Scilla * All parts Solanum * All green parts, berries Solidago Leaves Sorbus Berries Symphytum officinale All parts Tanacetum All parts Tulipa All parts Vinca All parts Zantedetchia All parts Scientific Name Toxic Agent(s) Aconitum * Diterpenoid alkaloids (aconite) Acorus calamus Asarone Aerculus Coumarin, Glycosides Agrostemma Saponins Allium giganteum Alkaloids Amaranthus Nitrates Amaryllis Alkaloids Anchusa Alkaloids Anemone Protoanemonin, glycosides Antirrhinum Purgativeve (alkaloid?) Aquilegia Alkaloids, thu'one Arisaema triphyllum Oxalic acid Artemisia * Alkaloids, sesquiterp enes Asdepias Alkaloids, resinoids, cardiac glycosides Asparagus Unidentified toxin Aster Selenium compounds Azalea Resinoids Baptisia Quinolizidine alkaloids Begonia Unidentified toxin Beta vulgaris *** Oxalic acid, nitrates Borago officinalis ** Alkaloids (lycopsamine, thesinine, amabiline) Browallia Alkaloids Brugmansia * Tropane alkaloids Caladium Oxalates Caltha palustris Protoanemonin Clematis Protoanemonin Colocasia Oxalic acid Convallaria majalis Cardiac glycosides (convallarin,convallatoxin) Convolvulus LSD-like hallucinogens Corydalis Isoquinoline alkaloids Cotoneaster Cyanogenic glycosides Craetegus Cyanogenic glycosides Cyclamen * Unidentified toxin Cynoglossum Alkaloids Datura * Tropane alkaloids, nitrates Daucus Nitrates Delphinium Diterpenoid alkaloids Dicentra * Alkaloids (protopine) Dictamnus * Alkaloids, furans, limonoids Digitalis * Cardiac glycosides Echinops Quinoline alkaloids Escholtzia Alkaloids Eupatorium Nitrates, pyrrolizidine alkaloids, toxic alcohol (tremetol) Festuca arundinacea Alkaloids Fritillaria Alkaloids Galanthus Alkaloids Gladiolus Emetic substances Gloriosa superba * Alkaloids Hedera helix Sa onins Helenium Glycosides (dugaldin) Heliotropium * Pyrrolizidine alkaloids (lasiocarpine, heliotrine) Hyacinthus Unidentified toxin Hydrangea Cyano enic glycosides Hypericume perforatum Resinoids (hypericin) Impatiens Unidentified toxin Ipomoea LSD-like hallucinogens Iris Alkaloids, resinoids Lactuca sativa Toxic latex compounds Lathyrus Varies with species Ligularia Pyrrolizidine alkaloids Lilium Emetic substances Linum Cyanogenic glycosides Lobelia Alkaloids (emetic) Lupinus * Quinolizidine alkaloids(ana yrine) Lycopersicon Steroidal alkaloids(solanine) esculentum Malus * Cyano enic glycosides Menispermum Alkaloids canadense Mirabilis jalapa Stomach irritant Monarda Furanocoumarins Myosotis Alkaloids Nicotiana * Alkaloids (nicotine) Narcissus Alkaloids Nierembergia Alkaloids Nymphaea, Nuphar Alkaloids Ornithogallum Alkaloids Paeonia Resveratrol lactiflora Papaver * Isoquinoline alkaloids(morphine) Parthenocissus Unidentified toxin virginianus Penstemon Selenium compounds Petunia Alkaloids Phaseolus lunatus Cyanogenic glycosides (linamarin) (causes favism) Phaseolur vulgaris Hemagglutinins, toxiclectins Philadelphut * Unidentified toxin Polygonatum Anthra uinones Portulaca Oxalic acid Prunus * Cyanogenic glycosides Pteridium aquilinum Thiaminase Ranunculus Promanemonin, glycosides Rheum * Oxalic acid Ricinus * Ricinoleic acid, ricin Rumex * Oxalic acid Salvia reflexa Nitrates Sambucus Alkaloids Sanguinaria Alkaloids canadensis Saponaria Sa onins Scilla * Cardiac glycosides Solanum * Steroidal alkaloids (solanine), nitrates Solidago Nitrates, (resinoids at flowering time) Sorbus Unidentified toxin Symphytum officinale Alkaloids (echimidine) Tanacetum Tanacetin Tulipa Tulipalin Vinca Alkaloids Zantedetchia Oxalic acid All parts = leaves, roots, flowers, fruits and seeds * = human fatalities have been reported. There are probably fatalities for some of the other species, but many jurisdictions do not require such deaths to be reported. ** In Germany in 1991 borage was banned from use in medicine and commercial products. *** Hundreds of livestock deaths reported from beet tops.