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University Library, University of Illinois at Urbana-Champaign

Plants Toxic to Animals

N

Nightshade (Solanum spp.)

Description

About 1,500 Solanum species exist in the world, and they include some of the most common garden plants such as potato (Solanum tuberosum L.) and eggplant (Solanum melongena L.). One of the species, Jerusalem cherry (Solanum pseudocapcicum L.) is grown as a house plant for its compact form and small round berries which turn bright red at maturity. The tomato (Lycopercison esculentum Mill.) is also a related plant. Included in this entry are descriptions of Black Nightshade, Bittersweet Nightshade, Silverleaf Nightshade, and Horse Nettle. Horse Nettle also has its own expanded entry, and other related species may be found under their own names.

Bittersweet Nightshade (S. dulcamara)

Bittersweet nightshade is also known as European bittersweet or climbing nightshade. This plant grows from rhizomes and is a slender climbing or trailing perennial reaching 6 feet in length. Leaves are alternate, ovate, simple or deeply lobed, 1-1/2 to 4 inches long, and pointed at the tip. Flowers are deep purple or bluish purple with flower stalk arising between the leaf nodes or opposite the leaves. Nearly round fruits turn red when mature and stay on the vines through mid winter.

Black Nightshade (S. nigrum)

Black nightshade is an annual herb with a tap root. Stems are erect and much branched reaching 3 feet tall. Leaves alternate, ovate or lanceolate, and long-stalked. The flower has 5 white petals, sometimes with a yellow inner star, and ranges from 1/4 inch to 3/8 inch across. Berries are round and about 1/4 or so inches across, green, and turn purplish to black when ripe. Immature berries and foliage are toxic, but ripe fruits are reportedly edible.

Plants commonly known as black nightshade may include two native species, American Black Nightshade (S. americanum P. Mill.) and Eastern Black Nightshade (S. ptycanthum Dun.), as well as S. nigrum which was introduced from Europe and is widely naturalized. Solanum ptycanthum may be more commonly found in the midwest since S. americanum appears to be more concentrated in the southern states.

Horse Nettle, Bull Nettle (S. carolinense) ​

A perennial with a deep taproot and rhizome below ground. Its stem and leaves have yellowish spines and sometimes are hairy. Leaves are alternate and ovate with irregularly wavy or lobed margins. Flowers appear in June to August, are light purple to white, 3/4 to 1 inch across, and in short racemes near the top of the plant. Petals are united with 5 points at the margin. Fruits are globose, about 1/2 inch in diameter and yellow when mature. Yellow or brownish seeds are numerous, and irregularly circular, about 1/8 inch across. 

Silverleaf Nightshade or White Horse-Nettle (S. elaeagnifolium)

This perennial herb gets its common name because of its silvery appearance caused by the numerous fine hairs. Its thick, lanceolate leaves are wavy and roughly indented (sinuate). The stems and parts of the leaves have short stiff spines. The flowers appear at the end of branches and have petals which are pale to deep blue or lavender in color.

Distribution

Bittersweet Nightshade (S. dulcamara)

An introduced species from Eurasia, this plant is found in moist ground of low woods, roadsides, fence rows and thickets. It ranges from Nova Scotia to Minnesota through much of the Midwestern states and south to Florida and Texas. In Illinois, this plant is commonly found in the north-eastern counties including Champaign.

Black Nightshade (S. nigrum)

The native species, S. americanum, is usually found in undisturbed habitats or moist open woodlands, stream banks, valleys, fields, roadsides and waste places throughout the east central United States from Maine to Florida and west to Minnesota, Nebraska and Oklahoma. It is found in almost all counties of Illinois. The introduced species, S. nigrum, is rare in Illinois but abundant in some places from Minnesota and the Dakotas to Oklahoma.

Horse Nettle, Bull Nettle (Solanum carolinense L.)

This plant is found in waste spaces or neglected fields, gardens, and roadsides from the Atlantic coast to Texas, north to South Dakota and as far south as Florida. It is a common weed in all counties of Illinois.

Silverleaf Nightshade or White Horse-Nettle (S. eleagnifolium)

Silverleaf Nightshade is found in large colonies in open woodlands, pastures, stream valleys, roadsides and disturbed or waste grounds in the Southwest from Missouri to Kansas, Oklahoma, Texas, Arizona, New Mexico and southwestern Colorado. This plant is found in a a few counties of Illinois, but a similar species (S. carolinense) is easily mistaken for this plant. 

Conditions of Poisoning

Poisoning by these Solanum species occurs primarily when animals are confined in overgrazed fields or where nightshade is abundant. The hazard of poisoning varies depending on the plant species, maturity of plants, and other conditions.

Generally, the leaves and green fruits are toxic. Ingestion of juice from wilted leaves may be especially toxic and sometimes deadly. Many cases of poisoning have been reported as a result of eating green berries. Green berries have produced severe intestinal, oral and esophageal lesions in sheep. Cattle reportedly seek out the berries of Solanum species and will eat the green plant, specially when other green forage is unavailable. Silverleaf nightshade (S. eleagnifolium) is exceptional in that the ripe fruit is more toxic than the green. S. eleagnifolium is toxic at only 0.1% of the body weight. Toxicity is not lost upon drying. Solanine content increases up to maturity. Solanine, except in potatoes, is reportedly destroyed by cooking. Potato (S. tuberosum) peelings contain the major portion of the toxic principle in the tuber, and leaves, sprouts and vines. Sun-greened potatoes are especially toxic. Spoiled potatoes and peelings also have caused severe poisoning. Cooking does not appear to destroy all the alkaloids in greened potatoes. Toxicity may vary with the soil, climate and other variables. Animals may browse potato plants or eat sprouted potatoes, leading to problems. 

Control

Animals should be kept away from fields with heavy infestation of nightshade. Plants should be mowed or pulled up while in flower, and burned. Remove green parts of potatoes before cooking, eat only ripe tubers.

Toxic Principle
  • Many contain the steroidal glycoalkaloid solanine. Upon hydrolysis, a sugar and the alkaloid solanidine are recovered. The free (unconjugated) steroidal alkaloid (the aglycone) is the primary form acting on the nervous system.
  • Other aglycones present may include dihydrosolanidine, tomatidine and strophanthidin. Toxic properties of these compounds are characteristic of saponins.
  • Some of these plants also have cardiac effects, e.g., Jerusalem cherry (S. pseudocapsicum) contains an additional alkaloid, solanocapsine, which produces bradycardia.
  • In some plants, atropine-like constituents predominate, e.g., potato (S. tuberosum), and some strains and stages of black nightshade (S. nigrum).
Clinical Signs

Clinical signs vary with irritant effect caused by the intact glycoalkaloid or saponin, and the nervous effects of the alkaloid. Irritant effects include hypersalivation, anorexia, severe gastrointestinal disturbances, with diarrhea that is often early and hemorrhagic. The nervous effects include apathy, drowsiness, depression, confusion, progressive muscular weakness, numbness, dilated pupils, trembling, labored breathing, nasal discharge, rapid heartbeat, weak pulse, bradycardia, central nervous system depression, and incoordination, often accompanied by paralysis of the rear legs. Coma may occur without other nervous signs. High doses may cause intestinal stasis and constipation. Hemolysis and anemia, possibly a result of saponins, have been reported, with renal failure in severe cases. Terminal signs include unconsciousness, shock, paralysis, coma, circulatory and respiratory depression, and death. The course varies from sudden death to 3-4 days of illness which may terminate in death or recovery. In less acutely poisoned animals, there may be yellow discoloration of the skin in unpigmented areas, weakness, incoordination, tremors of the rear legs, anemia, rapid heart rate and bloat.

O

Oleander (Nerium oleander L.)

Description

Oleander is an ornamental evergreen shrub that can grow to approximately 20 feet tall. Its leaves are simple and narrowly lanceoleate, and 3-10 inches long. Its flowers are tubular with five or more petals and are commonly pink, red, purple, or white. The fruit pods contain many seeds, each with a tuft of hair to aid in dispersal.

Distribution

Oleander grows commonly in the wild in the southern portion of the United States from California to Florida, and is also often grown as a cultivated plant in northern climates. It is extensively used in landscaping due to its resistance to drought, heat, wind poor soil conditions, and grazing.

Conditions of Poisoning

All parts of the plant are highly toxic when ingested, and drying does not decrease toxicity. Sap from the plant can cause skin reactions in allergic individuals, and the smoke produced by burning the plant is also toxic. Ingestion is the most common cause of poisoning, and poisoning generally occurs when animals are allowed to graze where oleander is abundantly present. The lethal dose of green oleander leaves for horses and cattle is 0.005% of the total body weight, and the minimum lethal dose for cattle is 50 mg/kg of body weight. Horses that were given 40mg/kg of body weight consistently developed severe gastrointestinal and cardiac signs of poisoning.

Control

Oleander plants can be removed by cutting the branches back and digging out the roots, but full removal may take time as any missed roots will continue to send up new shoots. Oleander is fast growing and tenacious, so any areas where a plant has been removed should be closely monitored for new growth and shoots should be cut back quickly. Caution should be used when pruning or removing oleander plants due to the toxic nature of the sap. Skin should be covered completely while working with the plant, a dust mask is recommended, and cuttings should not be burned.

Toxic Principle

Cardiac glycosides, specifically oleandrin, oleandroside, nerioside, and neriine.

Clinical Signs

Nausea, vomiting, drooling, abdominal pain, diarrhea (possibly bloody)dizziness, slowed or irregular heartbeat, dilation of pupils, drowsiness, death.

Animals Affected

Humans, cattle, horses, dogs, cats, birds

References Used

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

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=a532

https://plants.ces.ncsu.edu/plants/all/nerium-oleander/

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

P

Philodendron (Philodendron spp.)

Description

Philodendron plants come in a variety of shapes and sizes depending on the species. Philodendrons commonly have shiny, dark green, deeply lobed leaves that can be several feet long, but that is not true for all species. The popularly cultivated heart leaf philodendron (Philodendron hederaceum) grows as a vine with heart-shaped leaves that are 4-12 inches long depending on the age of the plant and have no lobes.

Distribution

Philodendron plants are natively tropical but are popular indoor plants due to their impressive foliage and low maintenance requirements. Some philodendron species may be seen in the in the wild in the southern United States, but it is more commonly encountered as a cultivated plant.

Conditions of Poisoning

Poisoning occurs after ingestion. All parts of the plant are poisonous, but the leaves have the greatest concentration of the toxin. Skin irritation can also occur after contact with the sap, but is generally minor.

Toxic Principle

Calcium oxalates.

Clinical Signs

Painful burning sensation accompanied by swelling of the lips, tongue, and throat when ingested. Drooling, vomiting (not in horses), difficulty swallowing or speaking, and diarrhea are also possible symptoms. Death can potentially occur from swelling of the windpipe, but is not commonly seen. Skin irritation can occur from contact with the sap.

Animals Affected

Humans, dogs, cats, horses

References Used

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

https://plants.ces.ncsu.edu/plants/all/philodendron-selloum/

http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b611

Pigweed (Amaranthus retroflexus L.)

Other common names: Carelessweed, Redroot, Red-rooted pigweed
Description

Pigweed is a stout, rapidly growing annual plant that can reach 3-4 feet tall. The stems are branched and hairy, and can be red to purple in color. The leaves of the plant are alternate, petiolate, ovate to lanceolate, and pointed at the apex. The flowers are light green and grow in dense spikes or panicles approximately 3-8 inches long. The taproot of redroot pigweed is bright red in color, and seeds are black and shiny.

Distribution

A variety of pigweed species grow throughout North America, with redroot pigweed (Amaranthus retroflexus) being the most common and typical of the genus. It can be found in cultivated and disturbed soils along roadsides and waste areas, and is also common in and around animal enclosures. Prostrate pigweed (A. blitoides), tumble pigweed (A. albus), and Palmer amaranth (A. palmeri) are also frequently seen and have similar characteristics to the redroot pigweed.

Conditions of Poisoning

Poisoning occurs when the plant is ingested. Pigs and cattle should not be allowed to graze in areas where pigweed is present, and plants should be removed if seen growing in or near animal enclosures.

Control

The plant spreads and grows quickly from wind-blown seeds, so effort should be taken to remove the plants from the desired areas before flowering and the areas should remain under close observation if mature plants are seen in the vicinity.

Toxic Principle

Significant quantities of oxalates and nitrates may accumulate in the plant over time, and other currently unknown toxic substances may also be present.

Clinical Signs

Swelling of and around the kidneys can be caused by oxalates in the plant, if present. Renal tubular nephrosis can occur and has most likely been the cause of death of affected animals in previous cases, and it has been seen even in cases where oxalates were not present implying that there is an unknown compound in the plant that is the cause. Nitrate poisoning can occur if the plant has accumulated nitrates over its lifetime.

Animals Affected 

Pigs, cattle

References Used

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

Poison Hemlock (Conium maculatum L.)

Description

Poison hemlock is a coarse biennial herb with a smooth, purple-spotted, hollow stem and leaves like parsley. It grows 3 to 6 feet tall and in late summer has many small white flowers in showy umbels. Its leaves are extremely nauseating when tasted.

Although sometimes confused with water hemlock, poison hemlock can be distinguished by its leaves and its roots. The leaf veins of the poison hemlock run to the tips of the teeth; those of the water hemlock run to the notches between the teeth. The poison hemlock root is long, white, and fleshy. It is usually unbranched and can be easily distinguished from the root of water hemlock, which is made up of several tubers. 

Distribution

Poison hemlock was introduced into North America from Europe, where it is native. It has become well established in all regions except desert. The plants are easily found along roadsides, on the banks of streams, ditches, and canals, and as a weed in fields. It is found in all parts of Illinois. 

Conditions of Poisoning

Animals allowed to graze pastures infested with this plant are most likely to be poisoned in early spring, when tender and succulent new leaves come from the root. Similar regrowth takes place in the early autumn. The root itself seems to be nearly harmless in spring, but later in the year all parts - roots, stem, leaves, and fruit - become extremely poisonous. It was the juice of poison hemlock with which the ancient Greeks killed Socrates. Many cases of human poisoning occur because the hemlock roots are mistaken for parsnips; the leaves, for parsley; and the roots and seeds, for anise. 

Control

Poison hemlock should be dug up and completely destroyed because it is dangerous to both animals and humans.

Toxic Principle

Piperidine (nicotinic) alkaloids in Conium include coniceine, coniine, N-methyl coniine, conhydrine, and pseudoconhydrine. The alkaloid content is variable with the stage of development and the stage of reproduction of the plant. During the first year of growth, the plant alkaloid content tends to be low. Plants in the second year, however, have alkaloid contents of approximately 1% in all plant parts. The alkaloid content is somewhat higher after sunny weather, as compared to rainy weather. The highest concentration of alkaloids occur in the seeds which can contaminate cereal grains. Coniine (2-propylpiperidine) and N-methyl coniine progressively increase in flowers and fruits, while coniceine decreases during plant maturation. In the vegetative stage - i.e. early growth - coniceine (W'-2 propylpiperidine) is the predominant alkaloid. Coniceine and coniine are the primary teratogenic alkaloids of Conium.

Clinical Signs

Susceptible species include cattle, pigs, elk, poultry, goats, sheep, and rabbits to some extent. Toxicosis has been experimentally reproduced in sheep and horses as well. Consumption of the plant may also affect the flavor and odor of the milk produced by the poisoned animal.

Systemic effects: After having eaten poison hemlock, animals may lose their appetites, salivate excessively, bloat, and have a rapid but feeble pulse. They also show evidence of muscular incoordination and appear to have great abdominal pain. Other signs include muscle tremors, frequent urination and defecation, recumbency, mydriasis, and "nervousness" followed by severe depression. In animals that die, breathing ceases due to respiratory paralysis before cardiac arrest. Convulsions, which occur in water-hemlock poisoning, do not follow the eating of poison hemlock.

Teratogenic effects: Birth defects due to ingesting poison hemlock occur in (at least) calves and piglets and may include crooked legs (crooked calf disease, arthrogryposis), cleft palate, and kinked tails. Arthrogrypotic skeletal malformations occur in calves when poison hemlock is ingested by pregnant cows between days 40 through 70 of gestation. Similar skeletal lesions occur in pigs between days 40 through 61 of gestation. Cleft palates can occur in piglets if pregnant swine ingest poison hemlock between days 30 through 45 of gestation.

Animals Affected

Humans, cattle, birds, sheep, goats, pigs, horses, dogs, cats

References Used

Vetter, J.  "Poison hemlock (Conium maculatum L.)." Food and Chemical Toxicology. 42 (2004):1373-1382. 

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

Poison Ivy (Toxicodendron radicans (L.) Kuntze)
(=Rhus toxicodendron L., Rhus radicans L.)

Description

Poison ivy is a perennial, woody plant that can grow as a climbing vine or as a low upright or trailing shrub. Leaves are split into three leaflets, alternate, glossy, hairless, and may be toothed or lobed. Leaves turn red in the fall. Climbing plants produce aerial roots that grasp the climbing surface, generally the bark of a tree. Flowers are small, greenish-white, and grow in hanging clusters. Fruits are yellowish-white waxy berries.

Distribution

Poison ivy is native throughout the United States and southern Canada, although it is less common on the West Coast where poison oak is more prevalent. It grows in a wide variety of soils and locations including waste areas, woodlands, thickets, roadsides, clearings, and fencerows. 

Conditions of Poisoning

Poison is typically delivered through skin contact with the plant, although indirect contact, such as touching an animal or object that has rubbed against the plant, will also deliver the toxin. All parts of the plant are poisonous, including the berries. Smoke from burning poison ivy can contain the toxin and affect people who are allergic to it.

Control

Plants and root systems should be carefully dug up while using plastic gloves and keeping skin fully covered. Plants should be disposed of in a plastic bag, and should never be burned. Herbicides specifically for poison ivy can be purchased, but may not be cost-effective when dealing with a large infestation. Other pesticides such as glyphosate can be used selectively on poison ivy plants, but care should be used not to spread the pesticide to desired plants. Sheep and goats can eat poison ivy without any known problems, so allowing them to graze in areas infested with poison ivy can also help reduce the presence of the plant.

Toxic Principle

Urushiol, an oily, resinous toxin found in all parts of the plant. Drying does not decrease toxicity.

Clinical Signs

Redness of the skin, irritation, itching, swelling, blisters. Symptoms may be severe.

Animals Affected

Humans. Animals are largely unaffected by poison ivy, so the primary concern is generally secondary contamination from an animal that has rubbed against the plant and is then touched by a person.

Reference Used

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

https://plants.ces.ncsu.edu/plants/all/toxicodendron-radicans/

http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/weeds/poison-ivy.aspx

Poke or Pokeberry or Pokeweed (Phytolacca americana L.)
(= P. decandra L.)

Description

Poke is an erect, branched, smooth herb with coarse, succulent, purplish stems; at maturity it is 3 to 10 feet tall. Its leaves, borne on short stalks, are alternately placed and ovate and are without teeth on their margins. Leaves grow up to about 5 inches long. Poke bears small white flowers on short flower stalks along separate branches at the growing tip of the plant and in the axils of the leaves. Each flower becomes a dark purple berry, flattened and spherical. The berries contain crimson juice and about 10 seeds each.

A perennial, poke comes up year after year from an enormous taproot but it is spread only by seed.

Distribution 

Poke is a herbaceous perennial and is native to North America. Though considered as a weed in Illinois, it is a source of food in some regions of the country. Its habitat ranges from the New England states to Florida and as far west as eastern Nebraska. Poke is frequent in open woods and occurs in waste places, along fence rows, about farmsteads, and in pastures if the soil is especially moist and rich.

Conditions of Poisoning

Cattle and sheep are the most susceptible species but poisoning occasionally occurs in horses, goats, and pigs. Animals may feed on poke plants, especially in the spring, when the plants are succulent. Where grass is short, the animals may browse so close as to get the top parts of the poke roots. Unless green herbage is very scarce later in the summer, animals will avoid the tops and berries.

Control

Animals should not be grazed in pastures infested with poke, especially in the spring or during dry, hot periods. The most certain way to eliminate poke from wooded pastures, where the plants are likely to be numerous and where it may be difficult or impossible to use chemical weed-killers, is to dig the individual plants out by their roots. As poke is spread only by seed, it is important to destroy the plant before flowering. 

Toxic Principle
  • Saponins, believed to be the primary toxic constituents, are present in the berry juice and other parts.
  • Other toxic constituents have also been identified including the alkaloid phytolaccine (in small amounts) and the alkaloid phytolaccotoxin, as well as a glycoprotein.
  • If used as food, the water in which it is boiled must be thrown away. 
Clinical Signs

The eating of nonfatal quantities of poke, perhaps of the shoots, may cause retching or vomiting after two hours or more. These signs may be followed by dyspnea, perspiration, spasms, severe purging, prostration, tremors, watery diarrhea (often bloody) and, sometimes, convulsions. If a fatal quantity is eaten, perhaps including roots, the above signs are followed by paralysis of the respiratory organs and other narcotic effects, culminating in the death of the poisoned animal.

In Pigs:

  • Unsteadiness, inability to rise, retching.
  • Jerking movements of the legs.
  • Subnormal temperature.

In Cattle:

  • Same general signs plus a decrease in milk production. 
Animals Affected

Cattle, swine

Purple Mint (Perilla frutescens)

Description

Purple mint is an annual herb that is sometimes grown ornamentally or to be used as an ingredient in certain dishes. The plant generally grows to be 1-3 feet tall and is erect and often branching. The stem of the plant is usually a burgundy color (though sometimes green) and hairy, and the leaves are simple, opposite, and are green or purple. The edges of the leaves are coarsely serrated, and the leaves can grow to be up to 5 inches wide and 7 inches long, wider at the base and narrowing towards the tip. The flowers are small and vary in color from white to purple, and grow in clusters on flowering branches of the plant.

Distribution

Purple mint is found in the southeastern to midwestern United States. It can grow as a weed in the wild and can pop up anywhere in a pasture, although it prefers semi-shaded locations such as near buildings, the edges of wooded areas, and near fencerows.

Conditions of Poisoning

All parts of the plant are poisonous, but particularly the flowering branches. Dried plants can still be toxic, but the majority of the risk comes from consuming the plant while fresh, especially if flowers or fruit are present. Poisoning is mainly a concern during the late summer and early fall when the plant is flowering and other grasses and forages may be in short supply. Cattle normally do not feed on purple mint unless other food is not available, so it is important to have a ready supply of quality feed on hand for the animals to eat instead during this time of the year, and grazing in infested pastures should be limited during the flowering period.

Control

Effort should be made to look out for and remove the plant in late spring and early summer. It is difficult to control the plant in late summer and early fall, which is also when it becomes the most dangerous to livestock. Plants should be removed before flowering as the flowers are the most toxic part of the plant and to also prevent seed production and dispersal. Mowing the plants before seeds are produced will help prevent further spread as well. Avoid creating feed from areas infested with purple mint.

Toxic Principle

Ketones.

Clinical Signs

Acute pulmonary emphysema, acute respiratory distress syndrome (ARDS), edema, death.

Animals Affected

Cattle, horses, ruminants

References Used

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

https://plants.ces.ncsu.edu/plants/all/perilla-frutescens/

https://extension.tennessee.edu/publications/Documents/W135.pdf

https://www.cfsanappsexternal.fda.gov/scripts/plantox/detail.cfm