Dr. Sharon M. Douglas Department of Plant Pathology and Ecology The Connecticut Agricultural Experiment Station 123 Huntington Street, P. O. Box 1106 New Haven, CT 06504 Phone: (203) 974-8601 Fax: (203) 974-8502 Founded in 1875 Email: [email protected] Putting science to work for society Website: www.ct.gov/caes POISONOUS PLANTS INTRODUCTION only attractive but also tastes sweet. The Poisonous plants have always been part of situation of plant poisoning of children is daily life. In the nineteenth century, quite different than with adults since poisonings due to plants reached near- children have great curiosity and will often epidemic levels as people often foraged for chew on anything within their reach, sources of food from natural plantings. especially attractive berries or fruit. Today, potentially dangerous plants can still Children are also less likely than adults to be found all around us. Poisonous plants are spit out unpleasant-tasting substances. frequently part of interiorscapes in homes as Since much smaller quantities are necessary well as in landscape plantings outdoors. to produce a toxic reaction in children, the This has become increasingly problematic as risks of poisoning due to ingestion are much more and more cultivated, exotic plants greater than for adults. However, regardless from throughout the world are introduced of age, reactions to poisonous plants vary into the landscape. Recent studies have with the individual and can be influenced by estimated that 3.5% of all poisonings in the diet, metabolism, and medications being United States are due to plants. taken. All types of native and introduced plants can The term “poisonous” designates many be poisonous including ferns, herbaceous kinds of reactions or effects. Among the plants, woody shrubs, and trees. key effects are allergic reactions (caused by Identifying plants that are poisonous is spores, pollen, or naturally occurring difficult since poisonous plants do not volatile compounds emitted into the air by appear distinctly different from their plants), skin rashes or dermatitis (caused by nontoxic relatives or counterparts. Many direct or indirect contact with allergenic or poisonous plants have such unpleasant tastes irritant compounds), skin photosensitization that most adults don’t chew them for very (caused by exposure to irritating or long before spitting them out. However, allergenic compounds), and internal some poisonous plants are not distasteful poisonings or irritations (from ingestion of and can even be sweet and, if eaten in large plants or plant parts). The general types of quantity, can cause serious problems. An poisoning and examples of plants example is the fruit of deadly nightshade, responsible for each are: blood poisoning Solanum dulcamara; the red berry is not (wild cherry, Prunus spp.), nerve poisoning (mushrooms), cardiac poisoning (foxglove, belladonna, are toxic. Additionally, many Digitalis purpurea), and skin irritation plants are only mildly poisonous or cause (poison ivy, Toxicodendron radicans). symptoms only in unusual circumstances such as when they are consumed in great WHY ARE PLANTS POISONOUS? quantity. The substances responsible for poisonings or toxic reactions originate from many Poisonous principles can be classified in different pathways within plants. However, many different ways based on criteria such most poisonous principles are considered to as the chemistry of the toxic compound or be secondary metabolites or by-products its effects on the victim. As follows is one from the essential functions of the plant. method for classifying poisonous principles These are compounds that aren’t considered into categories and an example of each: fundamental to the life of the plant. Although there are many theories as to why • Alkaloids- these are nitrogenous plants produce these nonessential compounds which are complex, compounds, one of the key theories physiologically active, typically taste maintains that plants have evolved to bitter, and are usually insoluble in water; produce these compounds in order to deter (poison hemlock, Conium maculatum) animals from grazing on them and to keep • Glycosides- these compounds produce insects from eating them. one or more sugars (glycones) and one or more toxic aglycones; they are Plants can differ by degree of toxicity and usually colorless, bitter, crystalline many references classify plants as solids; (English ivy, Hedera helix) extremely, moderately, or minimally toxic. • Minerals- this category of poisoning is However, it is difficult to categorize plants associated with high levels of particular with regard to their toxicity since this varies minerals in the soil or atmosphere and with the age of the victim (directly related to subsequent uptake by plants; levels of body weight) as well as other factors that these minerals are accumulated in the influence levels of toxic principles in plants plants such that they become toxic; such as environment and stage of plant among the minerals often associated growth. For example, young shoots of with toxicity are lead, copper, and pokeberry or pokeweed (Phytolacca arsenic; americana) are not poisonous but roots and • Oxalates- these consist of soluble fruit are poisonous. The level of a particular oxalates and oxalic acid; poisonings are toxic compound may also be quite variable often attributed to small crystals of within a plant or plant family. An example insoluble calcium oxalate which cause is the Nightshade Family. This family has oral irritation when ingested; (dumb many members that are considered cane, Dieffenbachia spp.) poisonous plants although not every member • Photosensitizing Compounds- these is poisonous or even every part of a single compounds are psoralens which result in poisonous plant contains the poisonous acute sensitivity of skin to sun or other ingredient. For example, the cultivated sources of light after exposure; psoralens tomato, Lycopersicon esculentum, is a are furocoumarins; (giant hogweed, member of the Nightshade Family but the Heracleum mantegazzianum) ripe fruit are nontoxic. In contrast, all parts • Phytotoxins (Toxalbumins)- these of Belladonna or deadly nightshade, Atropa compounds are toxic protein molecules Poisonous Plants S. M. Douglas 2 The Connecticut Agricultural Experiment Station (www.ct.gov/caes) that are similar to bacterial toxins in determined by the quality of the sample so it structure and reaction; (castor bean, is important to obtain as complete a sample Ricinus communis) as possible. This includes all of the parts of • Polypeptides and Amines- these are the plant that are available at the time: nitrogenous compounds such as flowers, fruits or berries, leaves, and twigs. phenylethylamine and tyramine; (mistletoe, Phoradendron spp.) Information to assist with plant • Resins- these are compounds that are identification based on specific plant often chemically very different but characteristics is available upon request. which share certain physical characteristics; these compounds melt or HELPFUL INFORMATION FOR burn easily, are soluble in organic IDENTIFICATION OF PLANTS BY solvents, insoluble in water, and don’t PHONE contain nitrogen; (wisteria, Wisteria Although the best way to accurately identify sinensis) plants is by direct examination of plant parts, there are circumstances where it is IDENTIFICATION OF POISONOUS prudent to attempt to identify a plant over PLANTS the phone that has been accidentally One of the most effective ways to prevent ingested. The following list provides poisonings due to plants is to know the information that is helpful to have available identity of plants in your home in order to achieve this goal: interiorscape, landscape, and nearby woods or forests and their potential for plant • What part of the plant was eaten? poisoning. When buying new plants for the • If fruit were eaten, what type of fruit was home or landscape, it is helpful to ask about it (e.g., berry, nut)? their potential toxicity at the time of • Size, color, nature of the fruit (e.g., purchase. If purchasing a new home, it is juicy, fleshy, firm, dry). prudent to identify and inventory the plants • Number of seeds or pits in the fruit. in the landscape. If you need assistance • Arrangement of the fruit on the plant with identification of any of the plants, you (e.g., single, in pairs, in clusters, on can contact The Connecticut Agricultural stalks, not on stalks). Experiment Station or a local nursery or • Were any other parts of the plant eaten garden center. When identifying any plant, (e.g., roots, leaves, twigs)? it is important to know the common name as • Appearance and growth habit of the well as the scientific name (Latin binomial) plant (e.g., small, large, herbaceous, since common names are often misleading woody, shrub, vine, tree). and imprecise. For example, the common • Where is the plant growing (e.g., field, names ground cherry, Jerusalem cherry, woods, hedge, roadside, garden, park, Chinese lantern, and strawberry tomato all bog)? refer to members of the genus Physalis. • Size, shape, and arrangement of the leaves (e.g., round, oval, pointed, If a plant has been accidentally ingested, prickly, type of teeth, if any, at leaf accurate identification of the potential margins) poisonous plant is critical to treatment. The ability to accurately identify a plant is often Poisonous Plants S. M. Douglas 3 The Connecticut Agricultural Experiment Station (www.ct.gov/caes) SELECTED TERMS USED IN PLANT IDENTIFICATION An understanding of botanical