Know Your
Poisonous and Non-Poisonous Plants

By
Alicia McWatters, PhD, CNC

A variety of plants supply our birds with nutritional benefits. In addition to the useful plants, there are many which are poisonous and can cause injury and illness in a wide range of ways. Biochemists classify plants according to their chemical structures, as well as their effects, both good and bad. A number of plants, and even those which we consider food plants, contain chemicals that can be harmful to our birds.

Each plant possesses a different chemical make-up. There are a number of chemical compounds produced in plants, including poisonous and non-poisonous ones. Some are poorly understood, difficult to classify, and the specific compound involved in a case of toxicosis may be unknown. Many poisonous plants contain more than just one type of toxic substance. Toxic substances in plants are often considered to be the byproducts of plant metabolism. As well as being toxic, some plants possess an unpleasant odor or bitter taste. These unattractive features of a plant are thought to be a natural protective factor against plant-eating animals, birds, and insects. While unripe or green, fleshy fruits may be poisonous, when these fruits become edible, the mature seeds can then be dispersed for future plant growth.

Toxins produced by plants are thought to not only protect those plants from plant-eating organisms, but some may also prevent the invasion of fungi or bacteria. Some toxins are only produced when a fungus or bacteria invade the plant tissues, while some compounds may bind beneficial bacteria in root nodules.

When a potentially harmful plant substance has been consumed in a small amount, the body normally eliminates it readily. Each bird is an individual in its level of tolerance to a particular toxic substance, so it is usually best to avoid the use of any plant, which is known to contain a high concentration of a toxic substance. However, due to the low body weight of birds, even a low concentration of a plant toxicant could pose a health risk, if it were consumed in a large enough quantity.

Wild birds may eat certain plant parts and experience no toxic effects, but this does not mean that these same plant parts are safe for our domestic birds. Some birds and animals have developed special enzymes that enable them to break down some toxic compounds into harmless ones. In general, animals and birds are more susceptible to toxins than humans and sometimes only a small amount of a toxic substance will result in adverse health effects. Additionally, what may be toxic to humans may not be toxic to birds and vice versa. However, many plant substances that are toxic to humans and livestock are also toxic to household pets.

Often the toxic substance is only concentrated in specific parts of a plant. In some plants the toxin is located in the fruits or seeds; in others, the toxin may be contained in the leaves or roots. Many plants with edible parts also contain toxic parts. So we cannot assume that just because the fruits or leaves of a plant are safe that the roots, flowers, or seeds are safe. Therefore, knowing the edibility of the specific parts of a plant is very important when deciding whether to use a particular plant as a food source.

It is important to acknowledge that even though plants are "natural" and "organic", this does not necessarily equate to "safe" and "healthful". Not only are common "safe" substances poisonous in increased doses ("The dose makes the poison"); but the toxic effects that plants produce vary with the species, health status, age of the individual(s), environmental conditions, such as the time of year, humidity, growth conditions, growth stage, and other factors also play a role in the hazards posed by toxic plants. Many toxic plants serve dual purposes, and in appropriate doses or forms can be useful. Many medicines are derived from plant sources and undoubtedly many more medicinal uses will soon be discovered.

There are approximately 20,000 species of seed plants that are native or have been naturalized in the United States and roughly the same number of cultivated ornamental and agricultural species occur here. Experimental evidence has proven that over 700 plant species are poisonous. Of these 700, very few are known to cause serious poisoning or to cause fatalities to animals and birds.

Individual plants and populations of plants vary in the relative concentrations of toxic compounds they contain. This natural variation has helped plant breeders over the generations to select and develop plant varieties with low concentrations of toxic substances. Some plants, which are edible today, were at one time too toxic to eat in any quantity. For example, tubers of the wild potato are considered poisonous because of their high solanine (a glycoalkaloid) content. Nowadays we can purchase a variety of edible potatoes, which are specifically grown to contain a low solanine content. Only the leaves, sprouts and green, chlorophyll-containing tubers are toxic. With this in mind, we can appreciate the pioneering work of the native South American farmers whose careful and selective breeding have developed potato varieties that are not only nutritious and palatable, but safe as well.

The ingestion of a toxic plant substance can cause a variety of symptoms -- gastrointestinal disturbances (i.e., vomiting, diarrhea, constipation), nervous system, immune system, and circulatory system disorders, liver or kidney damage, prevent cell division, lower blood sugar level, and interfere with normal blood clotting. Other substances found in certain plants can cause a variety of skin reactions simply from their physical contact – pain, redness, blistering, swelling, and nasal or eye irritation. There are various plants which when consumed, or when in close contact of, can result in allergies, such as respiratory distress, mouth and throat irritation, and a few which can result in death.

To prevent plant poisoning, be sure to correctly identify all plants and be certain they are non-toxic before they are placed in your bird’s environment. Place potentially poisonous plants well out of your bird’s reach or in a part of your home not occupied by your bird.

Certain plants or plant parts that are considered harmful, if eaten in the proper form, (i.e., cooked versus raw), may be rendered harmless and thus pose no danger. However, there are some plant toxins that are not reduced by cooking.

Pesticides and herbicides used on household or garden plants can render otherwise harmless plants non-edible and can cause toxic effects. Never harvest plants, branches, flowers, or berries from roadsides or near major traffic areas as they can accumulate toxic heavy metals, such as lead and cadmium. Some molds and mildews can grow on foods, which can also render them, toxic due to the presence of mycotoxins. Be sure that all nuts and seeds fed to your birds are free from fungi and bacteria, which is highly toxic if consumed. Store such foods in cool, dry places to reduce the chance of them becoming infected with these harmful toxins.

Our birds have the innocence and curiosity of a small child. Therefore, all things, which come in contact with their claws and beaks, should be thoroughly inspected and identified as safe before allowing them to hold, chew, and/or ingest them. This rule applies whether our birds are kept indoors or out.

Obtaining the information about which plants possess toxicants that are harmful to our birds is very important to prevent them from injury. It is also important to remember that any plant, which is consumed in large enough quantities, has the potential to be toxic!

--county extension service

--local poison control center

--nursery or horticultural center

--state agricultural school

--forest research center

--National Animal Poison Control Center - 1-888-426-4435 or 1-900-680-0000. The charge is $45.00 per case (VISA, MasterCard, Discover, or American Express only). NAPCC will do as many follow-up calls as necessary in critical cases and, if you wish, will consult with your veterinarian. Available 24 hours a day. Web site: http://www.aspca.org/site/PageServer?pagename=apcc

• identify the plant species in question.
• call your local avian veterinarian immediately and seek medical aid and advice.
• keep your bird warm, comfortable, and as stress-free as possible. Any additional stress will make matters worse.
• bring plant to veterinarian’s office for further inspection and identification.
• if bird vomits, save a sample and bring to your veterinarian’s office for examination.

Plant foods are composed of a large number of chemical compounds. Toxic effects may result from the consumption of a plant or plant part that contains a high enough concentration of a toxic substance. Cooking may reduce the toxicity of some of the plant foods listed below.

Alkaloids and glycosides comprise two major classes of plant toxins, both highly complex and diverse. Some other toxic principals found in plants are oxalates, tannins, phenols, alcohols, ketones, protein substances, volatile oils, phototoxins and cancer-causing plant substances. What follows is a summary of these toxic compounds.

Alkaloids - Over 4000 alkaloid compounds have been identified and they occur in about 15-20% of vascular plants and at least 40% of plant families. They are found in roots, seeds, leaves, bark, and stems and many are bitter tasting. Their pharmacological activity affects the nervous system. They are both potentially toxic as well as potentially medicinal.

Plant families with many alkaloid containing species include the amaryllis family (Amaryllidaceae), aster or composite family (Asteraceae or Compositae), lily family (Liliaceae), buttercup family (Ranunculaceae), and nightshade family (Solanaceae). Two very poisonous groups of alkaloids are in the yew family (Taxaceae) and Poison Hemlock (Conium spp.) in the celery or umbel family.

Once ingested, enzymes in the liver may chemically alter alkaloids. Sometimes they are rendered harmless; in other cases they may become lethal. It has been indicated that the alkaloids in certain plant species, Ragwort for example, produce compounds, which are harmful, rather than the alkaloids themselves causing harm. Symptoms common to alkaloid toxicity include gastrointestinal disturbances (i.e., vomiting, diarrhea) and central nervous system effects, (i.e., lack of coordination, convulsions, and coma).

Glycosides - Glycosides are more widely distributed in plants than are alkaloids. Many are non-toxic, but a substantial number do yield toxic compounds. For example, cyanogenic glycosides are compounds, which release hydrocyanic acid as a by-product of their breakdown, which may occur when a plant is ingested. Trace amounts of cyanogenic glycosides are found in over 800 plant species in 80 different families. However, only a relatively small percentage of species contain high concentrations leading to cyanide poisoning and these are mainly found in the rose and legume family. Here are a few examples:

Cyanides are produced by the breakdown of cyanogenic glycosides in certain plants. Cyanide producing compounds are found in flax (Linum usitatissumum), and in the leaves, seeds, pits, and bark of several fruiting trees i.e., plum, apricot, cherry, peach, nectarine (Prunus spp.), apple (Malus spp.), and pear (Pyrus spp.), as well as Yew (Taxus spp.), Bracken Fern (Pteridium aquilinum), and in certain varieties of lima beans (Phaseolus lunatus). The boiling of lima beans (in an uncovered pot) releases the hydrogen cyanide gases and renders them safe if fed in moderation. The digestive system is capable of breaking down small quantities of cyanides, but in larger amounts may quickly result in anxiety, loss of balance, vomiting, breathing difficulty, kidney failure, high blood pressure, increased heart rate, and if treatment is not begun, may lead to convulsions, coma, and death.

Anthraquinone glycosides are found in Aloes (Aloe barbadensis and related spp.) and Rhubarb (Rheum rhabarbarum) leaves… Cooking does not eliminate the toxins.

Cardioactive glycosides are found in Oleander (Nerium oleander), Foxglove (Digitalis purpurea) and Rhododendron (Rhododendron spp.). All parts are poisonous. Symptoms of toxicity include vomiting, bloody diarrhea, sleepiness, coma, and sometimes, respiratory paralysis and death from heart failure.

Another group of glycosides are the goitrogenic glycosides or glucosinolates. They are present in the Brassicaceae family of plants (e.g., broccoli, mustard, radish, kale, cabbage, cauliflower, brussel sprouts, turnip,…) and in soybeans, peanuts, and pine nuts. While these glycosides exist in all parts of a plant, they are mainly found in high concentrations in the seeds. If these foods were eaten in large quantities over an extended period of time they may inhibit the uptake of iodine by the thyroid gland and limit the production of thyroxine. Cooking the above foods will reduce their glycosides; however, they are harmless if fed raw (soybeans should be served cooked, sprouted or soaked for 24 hours in the fridge) in small quantities and will provide your birds with a plentiful amount of nutrients for good health.

There is ongoing research into the many beneficial chemical compounds found in members of the genus Brassica. These vegetables have been recognized for their ability to stimulate the immune system, and act as an antidote in cancer prevention. They contain an abundance of nutrients -- vitamins, minerals, trace minerals, amino acids, essential fatty acids, and other natural chemicals, such as sulforaphane, which may inhibit illness and disease.

Oxalic Acid and Oxalates - Oxalic acid and oxalates (a salt or ester of oxalic acid) are found in particularly large amounts in rhubarb stalks and leaves, spinach, and beet greens. Oxalic acid is the waste product of plant metabolism and is found in practically all plant families, usually in highest concentrations in older plants. Along with the plant’s age, the oxalate content varies with seasonal, climatic, and soil conditions.

Many plants, mainly in the arum family (Araceae) contain calcium oxalate crystals and can cause burning, swelling and can be greatly irritating to the mouth and throat if ingested, by puncturing the mucous membrane tissues. This can lead to constriction of the breathing passage. Other symptoms of poisoning may include vomiting, diarrhea, weakness, muscular twitching, temporary loss of speech, and in severe cases, convulsions, coma, and death. The following common house plants are high in oxalate content and other toxic components -- Dieffenbachias, Calla Lily, Caladium, and Philodendrons. These plants may also cause skin and eye irritation upon contact.

Another adverse effect of consuming large quantities of oxalate containing plant foods is that there lies the potential that the oxalic acid or oxalates may combine with calcium in the digestive tract to form insoluble calcium oxalate. This can lead to a calcium deficiency, thus causing symptoms of hypocalcemia -- impaired growth and the drawing of mineral from bone, resulting in osteomalacia or osteoporosis. Other symptoms of hypocalcemia are tetany, seizures, heart disorders, elevated blood cholesterol, and nervousness. Such health conditions are more likely to occur if a bird’s diet is deficient in calcium. Last, but certainly not least, if insoluble calcium oxalates are deposited in the kidneys and other organs, it would result in severe damage. Oxalate-containing foods are edible if fed in small quantities, preferably raw.

Tannins and Other Phenols - Phenols are acidic and form salts with alkaline compounds. Those of the various species of Toxicodendron known as Poison Ivy, Poison Oak, and Poison Sumac, cause serious allergic reactions in many people. Tannins are complex, astringent phenols, the active part being gallic acid, a polyhydroxylphenol. They are used in tanning leather. They bind proteins and inhibit the action of enzymes, and can rapidly stop cell functions. They occur in many tree barks and other plant structures. Tannins of the gallotannin class are present in the acorns, leaves, and shoots of Oaks (Quercus spp.) making them extremely bitter and potentially toxic. Even edible acorns, usually must have their tannins leached before they can be safely consumed.

Alcohols - Although toxic alcohols are rare in plants, Water Hemlock (Cicuta maculata and related spp.) contains a highly unsaturated higher alcohol, cicutoxin, as its main toxic compound and is considered the most poisonous plant of the North Temperate Zone. White Snakeroot (Eupatorium rugosum) and some of its relatives contain another toxic alcohol compound, tremetol.

Ketones - Ketones are rarely poisonous; however, pulegone, a ketone volatile oil found in European Pennyroyal (Mentha pulegium), is potentially harmful.

Proteins, Peptides, and Amino Acids - Many types of proteins, peptides, and amino acids occur in plants and some are toxic. All beans, some grains, and potatoes, in the raw form, contain toxins called lectins. Lectins are found throughout the plant kingdom. Many members of the Fabaceae family have been found to contain lectins. Although the highest concentration is in the seeds, they occur throughout the plant. Boiling beans, grains, and potatoes for 10 minutes, before simmering, destroys these lectins. An alternative to boiling beans and grains is to sprout them or soak them for 24 hours in the fridge.

Lectins are carbohydrate-binding proteins that cause agglutination of red blood cells, may affect the intestines and prevent absorption of nutrients. For example, the seeds of Castor Bean, (Ricinus communis), contain a highly toxic protein substance known as a plant lectin, a toxalbumin called ricin that is released when the seeds are chewed. Ingesting only one or two of these seeds can be fatal. The leaves are less poisonous. Another toxic lectin called ricinus agglutinin is known to coagulate and break down red blood cells. Symptoms of poisoning may be delayed from several hours to a few days after the seeds are consumed. Symptoms include severe gastrointestinal irritation, lethargy, shock, and convulsions, Other toxic lectins include: abrin, found in Rosemary Pea (Abrus precatorius); robin, found in Black Locust (Robinia pseudo-acacia); and a lectin found in Pokeweed (Phytolacca americana) which is a mitogen, affecting the activity of the white blood cells. In spite of the adverse effects of lectins, they may possess anti-cancer properties.

Another example of a toxic protein is thiaminase, the thiamine-destroying enzyme found in Bracken Fern (Pteridium aquilinum) and Horsetail (Equisetaceae arvense) and related spp).

Protease inhibitors (enzyme inhibitors) are proteins that are found mainly in raw beans, but they also occur in grains, seeds, nuts, potatoes, eggplant and onions and inhibit the action of enzymes that digest protein. Protease inhibitors cause the pancreas to increase its output of the protein-digesting enzymes (proteases). Cooking will neutralize the inhibitors in these foods and leave most of the nutrients intact. Sprouting beans and grains or soaking them for 24 hours in the fridge are alternatives to cooking them and will also neutralize the inhibitors and provide a nutritious enzyme-rich food. Under certain conditions, protease inhibitors are known to inhibit the growth of cancer.

Resins and Volatile Oils - Resins and volatile oils, also known as essential oils, are produced by many plants. Many are thought to be derived from terpenes. Mayapple (Podophyllum peltatum) contains a complex of toxic compounds known as podophyllum resin. These are bitter and highly purgative. Only the ripe fruit of Mayapple is edible. Podophyllotoxin and its derivatives have medicinal properties in cancer treatment.

Spurges, including Crown-of-Thorns, Poinsettia, and various other ornamental species (Euphorbia spp.) contain an irritant compound, phorbol, as a toxic component of their latex. Many members of the heather family (Ericaceae), including Rhododendrons and Azaleas (Rhododendron spp.), Mountain and Swamp Laurels (Kalmia spp.), and Pieris (Pieris japonica), contain terpenes also known as andromedotoxins that affect the circulatory system and the heart and are deadly. Other toxic terpenes are found in Daphne (Daphne mezereum and related spp.), Iris (Iris spp.), Marijuana (Cannabis sativa), and Chinaberry Tree (Melia azedarach).

Volatile oils are compounds, which are aromatic and evaporate when exposed to air. In small amounts their fragrance can be attractive, but in larger amounts can be harmful. Some can be tumor-producing. If plants containing thujone, a volatile oil, are used regularly, and in large quantities, they may produce behavioral changes, convulsions and brain cortex lesions. Thujone exists in the following plant species – Cedars (Thuja spp.), Junipers (Juniperus spp.), Cypresses (Chamaecyparis spp.); various species of the aster family, Wormwoods (Artemisia spp.), Yarrow (Achillea millefolium), and Tansy (Tanacetum vulgare).

Phototoxins - Certain plants contain chemical substances that may cause extreme skin sensitivity to the ultraviolet rays of the sun. These photosensitive agents are called phototoxins and they are a diverse group of compounds. They include the furanocoumarins, including psoralens, which are found in several plants of the celery family (Apiaceae) and thiophene compounds in certain species of the aster family (Asteraceae) and these plants can cause cell damage on contact. Symptoms include itchiness, swelling and redness. Others travel to the skin after ingestion, such as St. John’s Wort (Hypericum perforatum), Buckwheat (Fagopyrum esculentum) and Lamb’s Quarters (Chenopodium album) Other plants which may cause a phototoxic reaction include parsley (Cymopteris watsonii), parsnip leaves (Pastinaca sativa) and Yucca (Yucca spp.).

Cancer-causing Plant Substances - Certain substances increase the chance of cancer development and these plants should definitely be avoided.

Fungi, or molds, are known to produce many tumor-inducing substances. For example, aflatoxins are produced by certain molds (mainly Aspergillus flavus), which develop on improperly grown peanuts, grains, and seeds. These toxins are known as mycotoxins and are known to cause cancer of the liver and other tissues.

Ergot (Claviceps spp.), a grain-contaminating fungus, contains many alkaloids and amines, and has also been found to induce tumors in laboratory animals.

Pyrrolizidine alkaloids, occurring in Ragworts (Senecio spp.), Rattlebox (Crotolaria spp.), and Heliotropes (Heliotropium spp.) are liver and lung toxins and are suspected of being carcinogenic. The largest concentration of these alkaloids is in the seeds and flowers.

Safrole, a volatile oil, is present is many different flavorings and spices, especially the root bark of Sassafras (Sassafras albidum). The growth of liver tumors has been observed in laboratory rats that were fed large concentrations of this plant.

Cycads, or seed-ferns (Cycas spp.) are commonly grown as house ornamentals. They contain a series of glyosides, the main one being cycasin. Their seeds have been found to be highly carcinogenic when fed to laboratory animals.

Bracken Fern (Pteridium aquilinum) has been found to contain several cancer-causing substances (i.e. quercetin and kaempferol), as well as other toxins, in their green fiddleheads and rhizomes.

Onions (Allium cepa and related spp.) eaten in large amounts over a long-term period can result in anemia and digestive disturbances in humans and livestock. Onions, Chives, and Garlic contain several sulphur-containing volatile oils, which may cause irritation to the eyes, nose and skin.

Papaya (Carica papaya), Kiwi (Actinidia chinensis) and Pineapple (Ananas comosus) contain proteolytic enzymes, which may cause irritation to the mucous membranes if consumed in large amounts.

Aloe (Aloe barbadensis and related spp.) – the latex in Aloe leaves is toxic if ingested. It contains a number of anthraquinone glycosides, the prominent one is known as barbaloin. The quality and quantity of the glycosides varies from one species to another. Aloe vera contains high concentrations and also contains substantial amounts of chrysophanic acid. If excessive amounts of these compounds are ingested they may cause kidney irritation. The center flesh of the Aloe plant is safe.

Avocado (Persea americana) –pits, leaves, unripe fruit, and stems are toxic to many types of animals and birds. The Fuerte and Napal strains may be more toxic than others. Avocado toxicity may result in the following symptoms -- depression, tremors, lung congestion, and in some cases is fatal.

In spite of all that is known about plant chemistry, there is still so much more to discover. While some plants are indeed toxic, many plants are used for medicinal purposes as well as for their nutritive value. The continued study of plants and their multiple uses and benefits will provide us with even more knowledge to better the health of our birds.

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