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University Library, University of Illinois at Urbana-Champaign

Plants Toxic to Animals

R

Rhododendron (Rhododendron spp.)

Description

Rhododendron is a genus of a shrub with about 800 species worldwide. Its ovate evergreen or deciduous leaves are alternate, 1/2 - 8 inches in length depending on variety, with smooth untoothed margins. They are dark green with a glossy upper surface and a dull underside. Large trusses of bell-shaped flowers bloom from spring to early summer. Plants are available with flowers in colors such as white, purple, deep rose, red, yellow, and orange. Rhododendron and the closely related azalea have been hybridized for many uses in gardens and rarely reach above 3-5 feet tall in northern states including Illinois. 

Distribution

In Illinois, most species found are ornamental types that usually thrive in protected areas of gardens. Tall, wild varieties can reach over 35 feet high, and are found throughout the coastal mountain ranges from New York to Georgia. Designated as West Virginia's state flower, rhododendrons are particularly abundant in the Great Smoky and the Blue Ridge mountains. Species in the Pacific northwest from northern California to British Columbia vary in heights. 

Conditions of Poisoning

All parts of the plant, but especially the foliage, contain the poison, and consuming two or three leaves may produce severe toxicosis. Sucking flowers free of nectar may produce serious illness. Rhododendrons are more likely to retain green leaves year round than are most other plants, and therefore most cases of poisoning occur in the winter and early spring, when other forage is unavailable. 

Toxic Principle

All parts of this plant contain toxic resins (andromedotoxins, now commonly referred to as grayanotoxin) with the leaves being the most potent. Grayanotoxin produces gastrointestinal irritation with some hemorrhage, secondary aspiration pneumonia, and sometimes renal tubular damage and mild liver degeneration. 

Clinical Signs

Clinical signs usually appear within 6 hours of ingestion. Affected animals may experience anorexia, depression, acute digestive upset, hypersalivation, nasal discharge, epiphora, projectile vomiting, frequent defecation, and repeated attempts to swallow. There also may be weakness, incoordination, paralysis of the limbs, stupor, and depression. Aspiration of vomit is common in ruminants and results in dyspnea and often death. Pupillary reflexes may be absent. Coma precedes death. Animals may remain sick for more than 2 days and gradually recover.

Animals Affected

Dogs, cats, horses, cattle, sheep, goats, humans (from consumption of the plant, rhododendron tea, and/or honey made from rhododendron pollen).

References Used

Knight, A. P., & Walter, R. G. (2001). A guide to plant poisoning of animals in North America. Jackson, Wyo.: Teton NewMedia.

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/rhododendron

https://csuvth.colostate.edu/poisonous_plants/Plants/Details/111

Rhubarb (Rheum rhaponticum)

Description

Rhubarb is a perennial herb that is generally kept as a cultivated plant for use as a food item or as an ornamental plant either indoors or in a landscape. The leaves of the plant are large and heart-shaped with a thick, reddish petiole. Flowers are green to white, small, and grow in a dense panicle on the end of a flowering stem. Fruits are winged and reddish-brown when mature. Roots are large and fleshy.

Distribution

As a domestic plant, rhubarb is found all across the United States in homes, gardens, farms, and landscapes. Rhubarb is sometimes found in the wild as an escaped plant, and prefers moist, fertile soils.

Conditions of Poisoning

The toxin is transmitted through consumption of the leaves of the plant. The leaves are toxic when raw and the leaf blade remains toxic even after cooking and should never be eaten. The leaf stem contains less of the toxin and is generally safe to eat after being cooked, although consuming very large amounts (multiple pounds) of the cooked stems can cause symptoms of poisoning. Cooking the rhubarb with calcium carbonate will also help neutralize the toxin by converting the soluble calcium oxalates to insoluble calcium oxalates.

Toxic Principle

Soluble calcium oxalates.

Clinical Signs

Kidney failure, tremors, salivation, abdominal cramps, burning sensation in mouth and throat, headache, weakness, nausea, vomiting, coma and death if large quantities eaten.

Animals Affected

Humans, livestock, dogs, cats, horses

References Used

Knight, A. P., & Walter, R. G. (2001). A guide to plant poisoning of animals in North America. Jackson, Wyo.: Teton NewMedia.

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/rhubarb

S

Snakeroot, White (Eupatorium rugosum Hout.)
(formerly known as Eupatorium urticaefolium)

Description

White snakeroot is an erect, branched herb usually about 3 feet tall but varying from 1 to 5 feet. It has slender, round stems and branches bearing pointed, oval, oppositely placed leaves. These leaves, 3 to 5 inches long and petioled, are sharply toothed on the margins. Each leaf has 3 main veins that show prominently on the underside. The roots are fibrous, coarse, and shallow. 

 

Snakeroot with Flowers

In late summer, numerous small heads of minute white flowers appear at the top of the stem and the ends of the branches. These flower heads, except that they are white, are almost exactly like the flower heads of the familiar ageratum of gardens. Later the flowers are replaced in the heads by small black seeds each with a crown of soft white hairs.

Because the leaves of white snakeroot resemble those of the nettle, other plants with nettle-like leaves are often mistaken for it. Two such plants are the nettle-leaved sage and the nettle-leaved vervain. Even without flowers or fruit, these plants can be easily distinguished from white snakeroot. The nettle-leaved sage, a rare plant in some southern Illinois counties, has square stems; white snakeroot stems are round. The nettle-leaved vervain, a common weed throughout Illinois, has lance-shaped leaves; white snakeroot leaves are broad at the base but narrow quickly in a wedge-shaped part to the petiole.

Distribution

White snakeroot is found in woods of all types and along streams in wooded pastures throughout the Midwest. It persists after woods are cut, and often may be found many years after the land has been cleared, although usually in such areas it occurs only as scattered unthrifty plants. In prairie regions, it is not often found except in the woods bordering streams.

Conditions of Poisoning

An animal may die from eating either a large amount of white snakeroot at one time or small amounts over a long period. The eating of small quantities more or less continuously gives rise to the animal disease known as trembles. It is also the cause of the well-known and much-feared milk sickness of man -- a disease that is contracted from drinking milk or eating milk products from poisoned cows. Milk sickness claimed thousands of lives in the early 1800s, with perhaps the most well-known victim being Abraham Lincoln's mother. Nursing calves and lambs may die from mothers' milk that is contaminated with snakeroot even though the mother animals show no signs of poisoning. Cattle, horses, and sheep are the animals most often poisoned. 

Control

During the dry period of late summer, animals should not be pastured in woods or fields where there is white snakeroot. If the pasture is known to be infested, animals should be moved out of it within the first few days of July and should not be returned to it until the following year.

Eradication of white snakeroot is not easy. Chemical weed-killers cannot be used satisfactorily, because they endanger trees and other plants of the pasture. The best way to reduce the number of the plants is to pull them out by the roots and burn them; the best time to do this is in September, when the plants are more easily identified by their white blossoms. If the plants are pulled after a hard rain while the ground is soft, the shallow roots come out readily.

Toxic Principle
  • The apparent toxic principle in white snakeroot has been given the trivial name tremetol. It has been described as a fat-soluble, high molecular weight alcohol.
  • Crude tremetol, was later shown to be separable into a toxic ketone fraction (61%) (tested in goldfish) and a nontoxic sterol fraction (39%). The ketone fraction was later separated into tremetone, dihydrotremetone, and hydroxytremetone. These may all be components of a fragile tremetol molecule.
Clinical Signs

White snakeroot can endanger the lives of persons and animals other than those that have actually eaten the plant. Consumption of the plant may also affect the flavor and odor of the milk produced by the poisoned animal.

In Cattle and Sheep: 

Although animals that have fed on white snakeroot may be listless and somewhat inactive at first, the first noticeable manifestations of poisoning are loss of weight and trembling following exercise. Trembling is especially marked in the muzzle and legs. As poisoning progresses, cattle lose appetite, become constipated, lose weight, and gradually become weaker until they are not able to stand. Additional signs may include a peculiar odor to the breath and urine, excessive salivation, and quickened, difficult breathing. Later, complete relaxation without tremors and coma are seen, with death following in 2-10 days.

The clinical signs that are exhibited by poisoned sheep are similar to those shown by cattle. Death may occur in a few days or may be delayed.

In cases of chronic poisoning, post-mortem examination generally reveals extensive degenerative changes in the liver and kidney.

In Horses:

The onset of clinical signs in white snakeroot poisoned horses is within 2 days to 3 weeks after initial ingestion (usually after at least several days of ingestion). The major effects are related to congestive heart failure. Tremors are inconsistently observed in horses with white snakeroot poisoning. Horses may stand with legs wide apart. Sweating may be evident especially between rear legs, and stumbling in the rear legs may be noted when horses are turned. Severe depression, bloody urine, and/or choking may also occur. Sometimes swelling is present in the lower neck area, near the thoracic inlet. They may exhibit a jugular pulse and a rapid heart rate. Changes in electrocardiogram include increased heart rate, ST elevation, and variable QRS complexes, and ventricular premature beats. Cardiac arrhythmias are often present.

In Guinea Pigs:

The refusal to eat by the animal is the first sign, followed by listlessness and crouching with half-closed eyes. The hair becomes rough. Muscular tremors may not be noticeable, but complete lack of muscular coordination and stupor precede death. (White snakeroot poisoning, by R. Graham and V.M. Michael. Circular #436, University of Illinois College of Agriculture,1935.)

Animals Affected

Cattle, sheep, horses, guinea pigs

References Used

Knight, A. P., & Walter, R. G. (2001). A guide to plant poisoning of animals in North America. Jackson, Wyo.: Teton NewMedia.

St. John's Wort (Hypericum perforatum L.)

Description

St. John's Wort is an herbaceous perennial that is erect and grows up to 3 feet tall. It has many opposite branches and an extensive rhizomatous root system. The leaves are opposite, elliptic to oblong, and may have tiny, dot-like translucent or black glands. The flowers are bright yellow, star-shaped with five petals that have black dots on the margins, and have many stamens.

Distribution

St. John's Wort is found as a weed throughout most of North America, but it is particularly common in the northwest. It grows in dry, disturbed soils such as roadsides, fields, and waste spaces. It is also intentionally cultivated for use as an herbal medicine to treat depression, anxiety, and insomnia.

Conditions of Poisoning

Poisoning occurs after the plant is ingested and the animal is exposed to sunlight. Drying does not inactivate the toxin, so ingesting hay made from St. John's Wort can also produce symptoms. The young plants are as poisonous as the mature plants and seem to be more palatable to livestock. The amount of toxin present in the plant is dependent on the growing conditions of the plant and can vary.

Control

Animals should not be allowed to graze in areas where St. John's Wort is present, particularly animals with light skin or which lack a heavy layer of fur that will block sunlight.

Toxic Principle

Hypericin, which is a photoreactive pigment contained in the glands found on the leaves and flowers. The highest concentration of hypericin is found in the black glands, while the transparent glands contain protohypericin. Poisoning in cattle occurs after consuming about 1% of their body weight, while sheep must eat about 4% of their body weight to develop symptoms. 

Clinical Signs

Photosensitization, skin reddening, swelling, ulcers, sloughing of skin. Symptoms only develop when the poisoned animal is exposed to sunlight, and are generally limited to areas of the animal that are lightly pigmented or do not have thick fur to block sunlight.

Animals Affected

Humans, cattle, sheep, horses, cats, dogs

References Used

Knight, A. P., & Walter, R. G. (2001). A guide to plant poisoning of animals in North America. Jackson, Wyo.: Teton NewMedia.

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/st-johns-wort

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=e198

https://csuvth.colostate.edu/poisonous_plants/Plants/Details/43

T

Tulip (Tulipa spp.)

Description

Tulips are a popular spring ornamental that are often grown as an indoor or garden plant. The leaves of the plant are long, narrow, and alternate. The flowers often grow singularly and have six tepals that can be any of a wide range of colors except for true blue. The tepals often grow in the shape of a cup, although bowl, goblet, and star shapes also exist, and the edges of the tepals may have ruffles or fringe. The plant grows from a papery, teardrop-shaped bulb that resembles and is sometimes mistaken for an onion.

Distribution

Tulips can be found as cultivated plants across North America, but the plants can occasionally be found naturalized in the wild as well. Tulipa sylvestris can sometimes be found in fields, waste areas, and roadsides in the northeastern portion of the United States, and Tulipa clusiana has been seen in the southwestern United States in California.

Conditions of Poisoning

Poisoning can occur after consumption of the flowers, stem, or bulb of the plant, although the bulb has the highest concentration of the toxin. Skin contact can sometimes cause irritation, although effects are usually quite mild.

Toxic Principle

Tulipalin A and B.

Clinical Signs

Vomiting, hypersalivation, depression, diarrhea, stomach pains. Skin irritation is characterized by tingling, redness, and blisters that may spread beyond the point of contact, but effects are usually mild and brief.

Animals Affected

Humans, dogs, cats, horses

References Used

Burrows, George E., & Tyrl, Ronald J. (2013). Toxic plants of North America. Hoboken: Wiley-Blackwell.

https://plants.ces.ncsu.edu/plants/all/tulipa-spp/

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c252

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/tulip

W

Water Hemlock (Cicuta maculata L.)

Description

This 2-10 feet tall herbaceous perennial or biennial native of the Umbelliferae family is very difficult to separate from other species of the same family. It has a tuberous root with 2-8 oblong tubers which are 1.5-3 inches long and about 1/2 inch thick at the thickest point near the middle and stem end. The purple-streaked stems are stout and erect with much branching. The stems are solid when very young, but become hollow with nodes where the leaflets are attached. The stems are chambered with horizontal diaphragm of pith tissue which are more closely arranged at the base of the stem. The horizontal plates of piths are most easily visible by cutting the stem base lengthwise.

The alternate leaves are pinnately 2-3 times compound. The leaves of most species are lanceolate, 2-5 inches long, and sharply toothed. The base of the long petioles clasp the stem.

Flowers are white and tiny (no more than 1/8 inch across), have 5 petals, and appear in loose compound umbels at branch ends in mid summer. Umbels measure from 2 to 8 inches across and become somewhat spherical in fruit. Fruits are ovoid and ribbed on the outer surface.

New growth begins from tubers as well as from seeds. 

Distribution

The water hemlock occurs throughout the state of Illinois. It is occasionally encountered in wet pastures and meadows and frequently in and along ditches, in the low ground near streams, in low woods, and around ponds and lakes. 

Conditions of Poisoning

Water hemlock is among the most poisonous plants in Illinois. Although the leaves and fruit, either green or dried in hay, can be eaten without danger, a relatively small amount of the tuber will kill a cow in a short time. There is little danger during summer and fall as stock are not likely to browse on the tall coarse plants. But in early spring, the livestock will eat the young leaves and stems sprouting from the ground, and in doing so may pull the shallow tubers out of the soft wet ground and eat them also. 

Control

In the early spring livestock should not be allowed to graze in meadows infested with water hemlock, for the young shoots are then springing up and animals can easily pull the poisonous tubers from the wet, soft ground.

Pastures should be free of this plant. It is easiest to remove plants in the early spring. If the plant is not to be removed, it can be kept from spreading by mowing the tops before the seeds form. If extensive marshy areas become infested, it may be necessary to drain the land and cultivate it for several years before animals can again be safely pastured there. 

Toxic Principle

The toxic principle of water hemlock has been called cicutoxin and is a resinoid. It is a thick, yellow liquid with a carrot-like or raw parsnip-like odor. It is concentrated especially in the roots and the base of the stem at or below ground surface. The roots are toxic all year. Young leaves are nearly as toxic as roots, but mature leaves have been consumed in summer and autumn without associated problems.

Ingestion of two ounces of water hemlock tubers can kill a sheep, and eight to ten ounces of mature plant can kill a cow.

Clinical Signs

The clinical signs of water hemlock poisoning often follow a rather definite sequence. Frothing at the mouth may occur first, but this is quickly followed by uneasiness, frenzied movements, and other evidence of intense abdominal pain. Jerking of the muscles, twisting backward of the head and neck (opisthotonus), together with stiffening of the limbs, dilated pupils, and rolling eyeballs are followed by spasms of the diaphragm (in some species this may be associated with vomiting), convulsions, and death. The poison acts so quickly that the affected animal may die 15 minutes after the first abnormalities are noticed. 

Animals Affected 

Cattle, sheep

Wild Onion (Allium spp.)

Description

Wild onion (A. validum or A. canadense) is a bulbous herb of the Amaryllis family and is a close relative of cultivated onion (Allium cepa L.). It has a distinct onion odor. It has slender grass-like leaves and reaches about 2 feet in height when flowers appear in late summer. Leaves are narrow, long, and with parallel edges arising from the small underground bulb. Flowers, varying in color, depending on the species,  from white to pink, appear at the top of a leafless stem and eventually become bulblets which drop to the ground and propagate. 

It is thought that the name Chicago is derived from the smell of wild onions:

"Indians, mainly Potawatomi, who were the most powerful tribe around the south end of Lake Michigan, hunted, traded furs, and occasionally camped in the area they called "Checagou," evidently referring to the garlic wild onion smell which permeated the air." -- Encyclopedia of Illinois, 2nd. Edition. Somerset Publishers, New York, 1994. p. 138.

Distribution

Wild onion is found in meadows and woodlands in the northeastern and north central United States. Other species grow throughout the western United States. Several species of wild onion are found in Illinois with Allium canadense found in all counties. 

Conditions of Poisoning

Cattle are susceptible to onion poisoning and eating large amounts of this plant can cause death in this species. In areas where culled onions are grown commercially, they can be fed to cattle with few problems when the feed is mixed with ample amounts of other feed components. Poisoning may occur when cool spring weather delays growth of grass and wild onions are available in comparatively large amounts for cattle to graze. Horses and sheep are less susceptible, with goats being the least susceptible. In some cases, sheep may eat onions and show nothing more than slight hemoglobinemia. 

Control

Due to its easily-separable bulbs and thin, waxy leaves, wild onion can be difficult to remove both by hand pulling and through the use of herbicides. Using a trowel to dig up the entire bulb and roots can be effective and can help reduce the number of bulb and bulblets left in the ground. Steps to remove the plants should be taken during late fall in November and again in late winter/early spring before new plants are produced in March.

Toxic Principle

Both wild and cultivated onions contain the same toxic principle, N-propyl disulfide which primarily affects erythrocytes. The principle effects are related to hemolysis (rupture of red blood cells). This is believed to be secondary to oxidant-associated effects, and Heinz bodies may sometimes be evident in red blood cells. Other compounds are believed to be responsible for the lacrimator (tear producing) and antithrombotic (anti-clotting) effects associated with onions and garlic. Various sulfur-containing metabolites are probably responsible for the odors associated with ingestion of onions and garlic.

Clinical Signs

Urine discoloration may vary from wine red to almost black. Muscle weakness, rapid breathing, and a rapid heart rate may be noted if hemolysis is sufficiently severe. Some animals may be icteric (jaundiced) and/or have a characteristic onion odor to the breath. Loss of weight and appetite may also occur. Although severe toxicoses may be lethal, doses may cause only taste and odor problems in the milk of dairy cows.

Animals Affected

Cattle, cats, dogs, horses, sheep, goats

References Used

Knight, A. P., & Walter, R. G. (2001). A guide to plant poisoning of animals in North America. Jackson, Wyo.: Teton NewMedia.

https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/onion

https://lee.ces.ncsu.edu/2015/02/wild-onionwild-garlic-kill-control-prevent-it-2/