What are Poisonous Plants? 
The term poisonous plants refers to many kinds of plants that have a wide range of poisonous or disturbing effects. This app mainly deals with plants that cause chemical or physiological disturbances when taken internally.
There are other plants, that while not poisonous in the usual sense, can be dangerous because they cause mechanical irritation when eaten, photosensitization, or disagreeable tastes or odors in meat, milk, or milk products. These three categories are discussed briefly below.
Mechanical Injury
Some plants cause internal injury from sharp thorns, awns, or spines, or intestinal obstruction due to “hair balls” from various parts of a plant or needle-like crystals in the leaves. Wounds in and around the mouth may serve as areas of infection and can lead to starvation or weakness. Some of the important plants and their parts that cause mechanical injury are listed here.
Animals become extremely sensitive to light after eating certain plants. This can cause a variety of problems from redness and itching of the unpigmented or lightly pigmented areas of the skin to severe necrosis. Affected animals may die from starvation or other secondary effects. North Carolina’s most important plant in this category is Hypericum perforatum (common St. Johnswort), which contains hypericin causing primary photosensitivity. Secondary photosensitization is caused by liver dysfunction, which allows the accumulation of phylloerythrin (a normal breakdown product of chlorophyll) which in turn, causes photosensitivity. Plants that might cause liver dysfunction are Lantana, Vicia, and Crotalaria.
Disagreeable Tastes and Odors
A number of plants, poisonous and nonpoisonous, produce a disagreeable taste or odor in the milk, milk products, and occasionally meat of cows that graze these plants. Such tainted milk or meat is difficult or impossible to market. Some of the more important plants that cause this tainting are listed here.
Types of Poisonous Plants
Bacteria and Algae
Farm ponds and polluted streams sometimes contain toxic bacteria and freshwater algae. There are records of horses, cattle, hogs, sheep, dogs, and poultry fatally poisoned by drinking from ponds containing dense algal blooms. Although this source of toxicity is not common in North Carolina, it is still a possibility and should be guarded against.
A number of fungi, particularly certain mushrooms (toadstools), are poisonous to livestock and pets as well as humans. Although poisonous mushrooms are not treated in this app, they should not be overlooked as a possibility in cases of animal illness or death. Only a specialist, however, should attempt to distinguish poisonous from nonpoisonous species of mushrooms. Other fungi, such as ergot (Claviceps) on various grasses and others in moldy hay, should always be considered when poisoning has occurred. See Blackwell (1990) for a thorough discussion of poisoning from fungi.
Vascular Plants
The category “vascular plants” includes herbaceous and woody plants – such as ferns, lycopods, horsetails, conifers, and flowering plants – that make up what is generally thought of as the vegetation of an area.
The plants discussed in this app are all vascular plants and are arranged by family. Families are ordered more or less by their supposed evolutionary relationships. However, evolutionary or phylogenetic relationships can be depicted correctly only by a three-dimensional diagram, so any linear sequence such as that in a book is obviously artificial at various points along the sequence.
Conditions of Internal Poisoning
Dangerous Situations for Livestock
With few exceptions, grazing animals will not eat poisonous plants unless forced to do so by some unusual or artificial condition. The first means by which plant poisoning can be controlled, then, is by preventing the conditions under which these plants become dangerous. These conditions are listed below:
Starvation: Lack of good forage is the most common cause of plant poisoning. This occurs mostly in very early spring, late fall or winter, during droughts, or any time an area has been overgrazed.
Deficient rations: Livestock may graze poisonous plants if the animals lack required ingredients in the forage or if they maintain an unbalanced diet (one type of plant).
Waste and trash: Livestock should not have access to dumps where poisoning can occur. Clippings from the yard, garden, or houseplants may be extremely dangerous.
Newly plowed or exposed areas: Plowed fields, eroded ground, and new ditches can have exposed poisonous roots that otherwise would not have been available to livestock.
Dry or partially dry water holes: Poisonous roots may become exposed, seeds can germinate in the newly exposed soil, and increased numbers of bacteria or algae in the stagnant water can cause poisoning.
Incidental causes and curiosity: Many causes of poisoning cannot be related to a particular situation. Sometimes animals may incidentally or accidentally eat a poisonous plant while grazing other plants or by eating hay into which these plants have been mixed. Owners should also watch for poisonous plants growing outside of normal feeding areas. Out of curiosity or a need for variety in their diet, animals frequently graze around buildings or through fences; cattle, in fact, will graze through fences even when the best possible pasture is right at their feet.
Dangerous Situations for Pets
Although small animal pets are poisoned relatively infrequently compared to livestock, the potential for poisoning still exists in and around the home. With the animal population rapidly increasing in step with the human population, it is not surprising that poisoning of pets occurs more frequently and presents a serious and complex diagnostic and therapeutic problem for veterinarians. The growing popularity of exotic plants, some of which are poisonous to pets if eaten in sufficient quantity, has contributed to the rise in pet poisonings.
The great majority of poisoning in pets results from their ingesting the toxic material in food and water, although occasionally poisoning may result from absorption through a wound or even unbroken skin. Various chemicals used to control rabbits, foxes, rats, mice, and other pests can poison pets either directly if they eat the bait, or indirectly if they eat the sick or dead vermin that have eaten the poison. Pets can also be accidentally poisoned by various substances carelessly left out and available, such as chemical dips, dusts and sprays, kerosene, fumigants, soil sterilants, fertilizers, herbicides, expended clay pigeons, discarded storage batteries, marijuana, tobacco, and many others.
Because dogs and cats primarily eat meat, many people overlook the possibility of pets being poisoned by native and cultivated plants. This is a mistaken notion, for while it is true that approximately 90 percent of their diet is meat, the remaining 10 percent can be almost anything, including poisonous plants. If eaten in sufficient quantity, most plants poisonous to humans and livestock will also be toxic to puppies, and kittens, adult dogs and cats, caged birds, lizards, and other pets.
Pet birds, such as canaries, have been poisoned by various fruits and seeds of native and cultivated plants around the home. Wild fruits and seed should never be collected and given to caged birds. Puppies and adult dogs have been poisoned by poisonous mushrooms (toadstools), fruits such as balsam pear and nightshade, leaves of Schefflera, bulbs of hyacinth, amaryllis, narcissus (jonquil, daffodil), and autumn crocus, and castor beans in a necklace. Cats have been poisoned by eating English ivy, berries of asparagus and nandina, and the leaves of philodendron. The increased popularity of various philodendrons in the home has caused a parallel increase in serious illnesses and numerous deaths among cats. Tobacco in the form of cigars, cigarettes, pipe tobacco, or chewing tobacco can be dangerous to puppies, adult dogs, and birds. Mistletoe berries are poisonous and often available from this popular Christmas decoration.
There are several reasons why pets may eat various plant parts (leaves, flowers, fruits, seeds, bulbs) when available. Pets might be bored in confined areas, adapting to a change of environment, curious about newly introduced items such as houseplants or Christmas decorations, or undergoing behavioral changes. We do not advocate eliminating all known toxic plants from a household where pets live. However, pet owners should be aware of potential dangers and take the necessary precautions. Proper care of pets should include sensitivity to their eating habits and their general, everyday behavior. For more information see Fowler (1981).
Numerous factors influence the action of the poisonous substances and severity of the poisoning. Among these factors are (a) the quantity eaten, and over what period of time, (b) the chemical nature of the poison, (c) the source of the poison (part of plant and condition of the plant), (d) species of animal poisoned, (e) size, age, sex of the animal, and (f) the general health of the animal before eating the plant.
Using This App
Under each poisonous plant discussed in this app are a number of topics that deserve a word of explanation at this point. When looking for a poisonous plant it is best to check the questionable ones by the description, the illustrations, symptoms/clinical signs of the animal, habitat, and distribution in the state.
Description
Descriptions of the plants are brief and in many cases general; often, closely related species can be distinguished only by a specialist. Descriptive terms are explained in the glossary. Illustrations are given for those plants most likely to cause serious poisoning or death. Anyone in North Carolina may send in questionable plants for identification and information. Specimens can be sent fresh in a plastic bag, or pressed and dried between folds of newspaper for two to three days. Usually definite identification can be made only if the flower or fruit and an entire twig with leaves are sent in.
Send specimens to:
Vascular Plant Herbarium
Department of Plant and Microbial Biology, Campus Box 7612
North Carolina State University
Raleigh, NC 27695-7612
Habitat
The types of habitats in which the species is usually found are given. In general, a plant species is more or less restricted to a particular type of environmental condition, although some are found in many different habitats.
Distribution
The general range of each species is described and maps are given for those not found throughout the entire state. Shading on the maps indicates the general area in which the species grows. Written distributions usually are given in terms of the three physiographic provinces in North Carolina (Map 1). Note that the piedmont is subdivided here into upper and lower, relative to elevation rather than to north and south. Little can be said about the distribution of cultivated plants or those that escape cultivation, except to point out where they are usually found, since presumably most could grow throughout the entire state.
Group Number
Because conditions under which poisonous plants are eaten are so variable, and because there are so many factors influencing the degree of poisoning, any ranking or grouping of plants on the basis of their relative importance is purely arbitrary and subjective. Any one plant may be thought relatively unimportant and yet, under a certain set of circumstances, may cause the fatal poisoning of a whole herd of cattle.
For this reason, plants described here are not arranged by their relative importance. However, they are placed in one of six categories based on past history of poisoning in North Carolina. These six categories are as follows:
Group 1. Those that are most likely to cause serious poisoning or death.
Group 2. Those that may cause serious poisoning or death, but are eaten rarely by livestock.
Group 3. Those that may cause serious poisoning or death, but are uncommon in North Carolina.
Group 4. Those that cause only minor disorders or irritation.
Group 5. Miscellaneous cultivated plants of the house, field, and garden that may cause poisoning but are usually unavailable to livestock but may be available to house pets.
Not assigned. Plants for which a group number has not been assigned. This may occur when data are lacking or limited. Includes plants that may cause serious poisoning or death, as well as plants causing minor disorders.
Poisonous Principle
When known, the kind of poison is given. Often the type of treatment may depend on the type of poison. The different poisonous substances are described in a later section.
Parts of the Plant
Detailed pictures or drawings are provided, and the specific portions of the plant that are poisonous are named. Notes on this topic are given so that pet and livestock owners can see which parts may have been grazed. Also, in the case of flowers or seeds, the plants may be controlled by cutting or pruning early in the season.
Periodicity
Although most poisonous plants are dangerous throughout the year, or growing season, many are most dangerous during certain seasons. For example: heaths (laurel, fetterbush, and others) are dangerous during the winter because of their evergreen nature, which makes them one of the few types of green vegetation available. Water hemlock is most dangerous in early spring because it is one of the first green plants to appear; it becomes relatively coarse and unpalatable later in the summer. Some plants are toxic by accumulation; that is, fresh material or plants dried in hay or other feed can cause harm when eaten over a long period of time rather than when ingested in a single feeding.
Animals Poisoned
The most dangerous plants are usually poisonous to all livestock, but occasionally only poultry or swine or cattle may be affected by a particular species. Some animals, by nature of the way they eat, may graze a particular plant or plant part that is unavailable to other animals. Also, because of physiological differences among different kinds of animals, a plant may be readily grazed by deer, for instance, but be poisonous to cattle or horses.
Symptoms/Clinical Signs
There is disagreement in the literature about the various symptoms/clinical signs of poisoning. These are quite variable and are usually not specific for particular plants. Early diagnosis is important in controlling losses by poisonous plants. In cases of suspected poisoning call a veterinarian as soon as possible, and move the livestock from the area where the poisoning occurred. You should survey the stock often to catch symptoms early while a remedy may still be possible. However, most of the damage may have been done by the time the sick animal is discovered, and too often poisoning is only noticed after the animal has died.
Abortions in livestock are often caused by an animal eating some poisonous plant in sufficient quantity to cause abortion but not enough to kill the animal or even cause outward symptoms. Abortions in cows have been caused by Gelsemium, Phytolacca, Cicuta, Conium, and by nitrate poisoning.
Treatment
Call a veterinarian! Remove animals from pasture or their feed!
For all practical purposes, treatment of plant-associated poisoning is symptomatic and supportive and no generally accepted antidotal agents are available. There are some exceptions, such as the treatment for nitrate/nitrite poisoning. In many cases, however, there is no particular treatment recommended, and, generally, specific treatments and dosages of the many curative drugs have not been included here because they vary so greatly. In some cases the drugs used for treatment may even be poisonous in improper doses. Try to find and identify the poisonous plant, but leave the treatment to the veterinarian.
Necropsy
If an animal dies of unknown causes, it is wise to request that your veterinarian perform a postmortem examination. Finding the cause, by clinical signs, may lead to a definite diagnosis and may suggest a means of safeguarding the remainder of the herd. Information on necropsy is given for veterinarians.
Poisonous Substances
Poisonous substances can be categorized by their chemical nature. These poisonous principles are glycosides, alkaloids, oxalates, oils, minerals, nitrates, resins or resinoids, and other miscellaneous compounds.
Glycosides
These are complex chemical compounds that readily break down under certain conditions, yielding a sugar plus an aglycone which may be poisonous. Glycosides are found in a variety of plants. They are usually bitter and may be restricted to a particular plant part. There are several types of glycosides, the most common of which are listed here.
Cyanogenetic, which yield hydrocyanic acid (prussic acid) upon break-down. Death in these cases is usually very rapid and with few outward symptoms. Examples: Hydrangea, Prunus, Photinia, Sorghum, and Triglochin.
Saponic, which yield saponins. These are complex chemicals that generally cause gastric irriations. Examples: Aesculus, Agrostemma, Medicago, Phytolacca, and Sesbania.
Goitrogenic, which inhibits the formation of thyroid hormone. These are found in mustards.
Irritant Oils, such as mustard oils and others, are pungent, sharp tasting compounds found mainly in the seeds. Examples: Mustards, wild radish, Ranunculus, Actaea, and Caltha.
Coumarin, can be poisonous, but the degree of toxicity is questionable. In some cases, coumarin forms dicoumarol, which is a hemorrhagic agent. Examples: Aesculus and Melilotus.
Cardiac, are those which stimulate the heart. Many different ones have been identified, most from members of the Plantaginaceae (e.g., foxglove), Liliaceae s.l., and Apocynaceae.
Alkaloids
Alkaloids are complex, basic, water-insoluble compounds, some of which are very poisonous. They are very bitter to the taste. These mostly affect the heart and nervous system. Examples: Aconitum, Amianthium, Argemone, Buxus, Conium, Corydalis, Crotalaria, Delphinium, Dicentra, Gelsemium, Lolium, Taxus, Veratrum, and Zigadenus. Bulbs of Narcissus, Amaryllis, and Crocus also contain alkaloids.
Oxalates
Soluble and insoluble oxalates form calcium oxalate crystals, which can cause kidney damage. Hypocalcemia is implicated. In quantity, the oxalate produces dullness, depression, and finally death in a few hours. Examples of plants containing oxalates include: Rheum and Rumex. Oxalate crystals (raphides) in certain plants (Araceae, for example) may cause irritation to the mouth.
Oils
Several nonglycoside oils cause gastroenteritis, other irritant effects in the gut, and eventually death if consumed in a large enough quantity. Examples: Dysphania and Glechoma.
Minerals
Selenium and molybdenum are two poisonous minerals taken up by plants from the soil. They are of greatest importance in central and western United States, and are not a problem in North Carolina. Copper, lead, cadmium, and fluorine may be deposited on foliage from air pollution or taken up by plants from contaminated soil.
Nitrate poisoning
This is fairly common and occurs most frequently when there is a sudden change in an animal’s diet to plants with a high nitrate content. It may occur from certain crop plants (oats, corn, sorghum), rye grass, vegetables (turnip tops, radish, carrot, lettuce), weeds (Amaranthus, Chenopodium, mustards, composites, nightshades), or silage or fodder with high nitrate content such as alfalfa. Heavy fertilizing can increase nitrate contents and the potential danger. Nitrate is reduced to nitrite, which oxidizes hemoglobin; this process causes vasodilation and sudden death. Postmortem diagnosis of acute nitrate poisoning is by the brownish discoloration of mucous membranes and internal tissues. The blood is chocolate colored in contrast to the bright red color indicative of cyanide poisoning.
Resins or Resinoids
These compounds are often extremely poisonous. They are direct irritants of the nervous system. Examples: Asclepias, Cicuta, Kalmia, Melia, and Rhododendron.
Control of the Plants
Usually the first question that arises after a poisonous plant is found in a pasture is how to eradicate it. The control or eradication of the species depends on the local conditions: how extensive in area, type of habitat, the age and size of the plants, and many other factors.
Because control measures vary so much, it would not be practical to provide specific suggestions here. You should contact your county agricultural agent or the extension weed specialist for the latest technique available for the type of plant growing under local circumstances. Some general methods of control are listed here.
Destroying
You can destroy plants by digging them up, burning, cutting, or by using chemicals. Be aware, though, that certain herbicides temporarily increase the palatability of foliage, and some poisonous plants are more dangerous in the wilted condition brought on by chemicals. Animals should be removed from the area to be treated until all suspect plant materials have been defoliated or removed.
Fencing
Fencing off areas where poisonous plants grow is often more practicable than destroying plants when they are abundant over a large area. Take care to keep poisonous plants out of reach of cattle grazing though the fence.
Good Management
Too often a pasture is treated as just a piece of land with a fence around it. Practice pasture fertilization and management that will maintain good grass sod. Usually, undesirable plants cannot compete with a well-developed grass sod. Most plant poisonings of livestock in pastures are attributable to plants found around buildings, fences, streams, ponds, spring heads, wooded areas, or dump heaps.