Poisonous Plants Commonly Found in Woodlands

There are a number of plants in Iowa's woodlands which may be poisonous to livestock. Some of these plants will only make animals delirious; others will kill them. For some plants, only certain parts of the plants are poisonous. The plants may not be poisonous to all livestock. The following table provides a listing of common poisonous woodland plants. It provides information about the toxic substance, the animal's symptoms, the parts of the plants that are poisonous and which animals have been known to be affected by the plant. This information may help your veterinarian diagnose poisoned livestock.

Bracken Fern (Pteridum aquilinum) & others:

Identifying Characteristics: Single stem with 3 fronds (fern leaves) in a triangular shape. Can be over 3 feet and tend to grow in large colonies

Poisonous Principle: Thiaminase (in horses), unidentified in cattle

Symptoms: Cardiac irregularities;

  • Weight loss, mucus, appetite loss
  • Incoordination
  • Convulsive
  • Death in 4-8 days

Poisonous Plant Part: All of the plant, especially leaves

Animals Affected: Horses, cattle, sheep

Buttercup (Ranunculus acris

*Note: Dried buttercup is not poisonous

Identifying Characteristics: Smooth stems, leaves are compound with 3 extremely lobed leaflets, yellow flower with petals

Poisonous Principle: Higher alcohol (anemenol)


  • Irritant
  • Decrease in milk production
  • Diarrhea
  • Nervous twitch
  • Convulsions

Poisonous Plant Part: Leaves

Animals Affected: All Animals

Climbing bittersweet (Celastrus scandens)

Identifying Characteristics: Woody Stemmed vine winding around other vegetation, simple oval shaped leaves, white/green flowers tha produce bright orange fruits when ripe

Poisonous Principle: Euonymin (not definitely known)


**Not fatal

  • Nausea
  • Prostration

Poisonous Plant Part: Leaves

Animals Affected: Horses, sheep, cattle

Cocklebur (Xanthium sp.)

Identifying Characteristics: Leaves are spirally arrangedaround a green stem, the seed cases are hardy and spiny and usually spherical

Poisonous Principle: Carboxyatractyloside


  • Vomiting, weakness, ataxia, subnormal temperature
  • Spasmodic contractions of limbs and neck
  • Death in 4-8 days

Poisonous Plant Parts: Small plants, seeds

Animals Affected: Mainly hogs and cattle, but possible for other animals

Dutchman's breeches (Dicentra cucullaria)

Identifying Characteristics: Stems are pinkish-green, leaves can be 4 to 14 inches long and 1 to 7 inches wide with 3 budding from one spot, these leaves have finely divided leaflets, and flowers are pink to white with 2 obvious points pointing upwards

Poisonous Principle: Alkaloid (Cucullarine)


  • Spinal cord (convulsion) trembling
  • Salivation
  • Vomiting
  • Convulsions

Poisonous Plant Part: Plants, especially tubers

Animals Affected: Cattle, horses

Horsetails or Scouring Rushes (Equisetum sp.)

Identifying Characteristics: Typically leafless and flowerless plant that has segmented stems. These stems are rough feeling and used to be used for scouring while cleaning. These are usually found near water

Poisonous Principle: Thiaminase


  • Maintained Appetite
  • Excitability 
  • staggering
  • Diarrhea 
  • Convulsions
  • Coma
  • Death in 2 hours to several weeks

Poisonous Plant Parts: All parts

Animals Affected: Sheep, cattle, (horses less susceptible)

Jack-in-the-Pulpit or Indian turnip (Arisaema triphylum)

Identifying Characteristics: One or two leaves with 3 leaflets on their own stem, the flowering body is on a separate steam and "cloaked" by a hood-like leaf surrounding the flowering body

Poisonous Principle: Calcium oxalate crystals possibly alkaloid


  • Burning sensation in the throat, mouth, and stomach
  • Colic

Poisonous Plant Part: Corms/tubers

Animals Affected: Cattle, sheep, goats, hogs

Jimson weed or Devil's snare (Datura stramonium)

Identifying Characteristics: Foul-smelling, branching herb that can form into a bush. Leaves are 3 to 8 inches long, smooth and toothed, upper surface is dark green and the underside is light green. Flowers are white to violet and trumpet shaped.

Poisonous Principle: Alkaloid (Hyoscyamine)


  • Delirium
  • Dilated pupils
  • Muscular twitching
  • Frequent urination
  • Convulsing and coma precede death

Poisonous Plant Parts: All parts, especially seed and leaves

Animals Affected: Humans, livestock

Larkspur (Delphinium sp.)

Identifying Characteristics: Green, hollow stem, which differentiates it from monkshood. Larkspur flowers are purple to blue and grow on the top third of the plant. Leaves alternate and are deeply lobed and narrow.

Poisonous Principle: Alkaloid (Delphinine)


  • Heart and nervous system weakness
  • Twitching of muscles
  • Back arched
  • Nausea, vomiting, constipation and bloating

Poisonous Plant Parts: All parts, especially roots

Animals Affected: Cattle, hogs

Nightshade (Solanum americanum)

Identifying Characteristics: Herbaceous plant that can get several feet high. Leaves alternate and vary in size, they are coarse feeling and toothed along the edge. Flowers are white to pink/purple, with bright yellow stamens in the middle, fruit are shiny black berries.

Poisonous Principle: Glycoalkaloid


  • Anorexia
  • Vomiting, dirrhea
  • Pupil dilation
  • Death from respiratory paralysis

Poisonous Plant Part: Foliage and green berries

Animals Affected: Sheep, goats, chickens, ducks, hogs

Poison Hemlock (Conium maculatum)

Identifying Characteristics: Herbaceous plant with smooth, green, hollow stem. Stem can be streaked with red or purple on the lower half. Leaves are compound with 2 to 4 leaflets that look lacy and overall are triangular in shape. Flowers are small, white, clumped together.

Poisonous Principle: Alkaloid (Coniine)


  • Heart depressant
  • Paralysis
  • Coma
  • Death from paralysis of respiratory muscles

Poisonous Plant Parts: All parts, especially seed and leaves

Animals Affected: Humans, livestock, poultry

Squirrel Corn (Dicentra canadensis)

Identifying Characteristics: Similar looking to Dutchman's breeches, smaller in size, and has more of a heart-shaped flowers, only prominent in spring and goes dormant in the summer

Poisonous Principle: Alkaloid (Cucullarine)


  • Spinal cord convulsion

Poisonous Plant Parts: All parts, especially tubers

Animals Affected: Cattle, horses

White snakeroot (Equpatorium rugosum/ Ageratoma altissima)

Identifying Characteristics: Can be 3 to 5 feet tall. Blooms small white flowers in clusters from late summer to late fall. Leaves are oval shaped with large toothed edges similar to nettles

Poisonous Principle: Trematol


  • Nervous system
  • Tremors
  • Incoordination
  • Weakness
  • Often fatal

Poisonous Plant Parts: Any part above ground

Animals Affected: Cattle, horses, humans via milk from cows

Black locust (Robinia pseudoacacia)

Identifying Characteristics: Tree with compound pinnate leaves with even pairs of leaflets and one at the end of the leaf. Has thorns along branches where buds tend to be

Poisonous Principle: Phytotoxalbumin (Robin)


  • Delirium
  • Diarrhea
  • Death by cardiac failure

Poisonous Plant Parts: All parts, especially inner bark, even water where seed pods are lying

Animals Affected: Humans, livestock

Buckeye (Aesculus sp.)

Identifying Characteristics: Tree with usually large palmate leaves and can have showy flowers. Seed capsules can have prickles or spines.

Poisonous Principle: Glucoside (Aesculin)


  • Irritant with nervous symptoms of delirium
  • Incoordination
  • Rarely fatal

Poisonous Plant Parts: Seeds and younger shoots and sprouts

Animals Affected: Humans, cattle, swine, horses, sheep

Kentucky Coffeetree (Gymnocladus dioica)

Identifying Characteristics: Tree with double pinnate compound leaves and back is an ash color and flaky

Poisonous Principle: Alkaloid (Cytisin)


  • Irritant with nervous symptoms
  • Diarrhea with considerable straining
  • Death

Poisonous Plant Parts: Leaves, fruit

Animals Affected: Humans, livestock

Oaks (Quercus sp.)

Identifying Characteristics: Tree or shrub, leaves are alternately arranged with lobed margins, some, like chinkapin oak, have serrated margins. Acorns can vary in size.

Poisonous Principle: Tannin (quercitrin, and quercitin)


  • Anorexia
  • Excessive thirst
  • Frequent urination
  • Diarrhea
  • Death in 2 weeks to 1 month, usually only if large amounts are eaten

Poisonous Plant Parts: Young leaves, acorns, water where oak leaves are soaking

Affected Animals: Cattle, sheep, pigs

Wild Cherry (Prunus sp.)

Identifying Characteristics: Tree or bush, with simple oval shaped leaves. Leaves tend to be a shiny dark green on top and a lighter green on the underside with serrated margins. 

Poisonous Principle: Cyanogenetic Glucoside (Amygdalin)


  • Spinal cord convulsion
  • Breathing through mouth
  • Muscle spasms
  • Convulsions and with within 10 minutes
  • Death results from internal asphyxiation

Poisonous Plant Parts: Leaves and twigs, especially if foliage has wilted

Animals Affected: Livestock

Yews (Taxus sp.)

Identifying Characteristics: Coniferous tree or shrub, with reddish bark and flat dark green needle like leaves. The fruiting body is a bright red color

Poisonous Principle: Taxine


  • Nervousness
  • Incoordinations
  • Collapse
  • Gastroenteritis
  • Death from cardiac failure

Poisonous Plant Parts: All parts

Animals Affected: Humans and all livestock

This article is a web-based modification of the original publication "F-351 Poisonous Plants Commonly Found in Woodlands" prepared by former ISU Extension Forester Paul H. Wray.