Poisonous Plants In Colorado

When you’re enjoying the outdoors in Colorado, it’s important to be aware of the local flora that can cause harm. Understanding the poisonous plants in Colorado is key to a safe adventure for you, your family, and your pets.

Colorado’s landscapes host several poisonous plants, including water hemlock and certain lupines, which pose risks to people and livestock. This guide will help you identify them and know what to do if contact occurs.

This section provides a detailed overview of the most common toxic plants found across the state. We’ll cover identification, toxic parts, and the symptoms they cause.

Water Hemlock (Cicuta Douglasii)

Often called the most violently toxic plant in North America, water hemlock is found in wet areas like stream banks and marshes. It’s a perennial that can grow over six feet tall.

The entire plant is poisonous, but the roots contain the highest concentration of cicutoxin. This toxin attacks the central nervous system.

Identification: Look for smooth, hollow stems with purple streaks. The leaves are compound and toothed. Small white flowers grow in umbrella-like clusters.
Symptoms: Symptoms appear quickly and include excessive salivation, tremors, seizures, and potentially respiratory failure.
Action: This is a medical emergency. Seek immediate veterinary or human medical attention if ingestion is suspected.

Death Camas (Toxicoscordion Venenosum)

This plant is deceptively dangerous because it resembles edible camas and onions. It grows in meadows, sagebrush slopes, and aspen groves.

All parts of death camas are toxic, containing alkaloids that affect the heart and nervous system. It is particularly a threat to grazing livestock.

Identification: It has grass-like leaves and a cluster of creamy white flowers at the top of a single stalk. It does not smell like an onion when crushed.
Symptoms: Symptoms include nausea, vomiting, weakness, slowed heart rate, and in severe cases, coma or death.

Monkshood (Aconitum Columbianum)

Also known as wolfsbane, this striking plant is found in moist, high-altitude areas. It’s often seen in subalpine zones near streams.

Every part of the monkshood plant contains aconitine, a potent neurotoxin and cardiotoxin. Even handling the plant without gloves can lead to skin absorption.

Identification: Recognizable by its distinctive helmet-shaped blue or purple flowers. The leaves are deeply lobed and palmate.
Symptoms: Initial symptoms include burning in the mouth, nausea, and vomiting. This can progress to muscle weakness, heart rhythm problems, and paralysis.

Poison Hemlock (Conium Maculatum)

This invasive biennial is found in disturbed areas, roadsides, and ditches. It’s important not to confuse it with water hemlock, though both are extremely dangerous.

The plant contains coniine alkaloids, which cause a progressive paralysis of the muscular system.

Identification: It has smooth, hollow stems with distinctive purple blotches. The leaves are fern-like, and the flowers are small and white, arranged in umbrella clusters. It can smell musty or like mouse urine.
Symptoms: Symptoms often begin with trembling, coordination loss, and slowed heart rate, progressing to respiratory failure.

Oleander (Nerium Oleander)

While not native to Colorado, oleander is a common ornamental shrub planted in landscapes. It is highly toxic and all parts are poisonous, even when dried.

The toxins are cardiac glycosides, which disrupt the heart’s rhythm. A single leaf can be lethal to a child.

Identification: An evergreen shrub with long, narrow, dark green leaves. It produces showy clusters of white, pink, or red flowers.
Symptoms: Symptoms include severe digestive upset, irregular heartbeat, drowsiness, and potentially death.

Locoweed (Oxytropis And Astragalus Species)

This is a group of plants that pose a chronic threat to livestock, particularly horses and cattle. They grow in dry, rocky plains and foothills.

The plants contain swainsonine, which causes a neurological condition called “locoism” when consumed over time.

Identification: They are low-growing perennials with purple, pink, or white pea-like flowers. The leaves are typically compound.
Symptoms in Animals: Animals become depressed, lose coordination, exhibit strange behavior, and may suffer from weight loss and eventual death.

Certain Lupines (Lupinus Species)

Not all lupines are toxic, but many species in Colorado contain alkaloids. They are a significant cause of birth defects in livestock if ingested at certain stages of pregnancy.

The seeds and pods contain the highest concentration of toxins. The danger is primarily to animals, but can also affect humans.

Identification: Lupines have familiar palm-shaped leaves and tall spikes of pea-like flowers in various colors like blue, purple, and yellow.
Symptoms: Acute poisoning causes nervousness, depression, and respiratory difficulty. The chronic issue is “crooked calf syndrome” in cattle.

Mountain Laurel (Kalmia Microphylla)

This native evergreen shrub is found in wet, acidic soils in mountainous regions. It’s also known as bog laurel.

The leaves and nectar contain grayanotoxins, which affect sodium channels in the body. Honey made from the plant (“mad honey”) can also be toxic.

Identification: It has small, leathery leaves arranged opposite each other on the stem. The flowers are pink to rose-colored and saucer-shaped.
Symptoms: Symptoms include excessive salivation, nasal discharge, vomiting, weakness, and slowed heart rate.

Baneberry (Actaea Rubra)

This woodland plant is found in shady, moist forests. It has attractive but highly toxic berries.

The berries and roots contain cardiogenic toxins. The berries are especially tempting to children due to their bright red or white color.

Identification: It has compound leaves with toothed edges. The plant produces a spike of small white flowers in spring, followed by shiny berries on a thick red stalk in late summer.
Symptoms: Ingestion causes dizziness, stomach cramps, headache, and potentially cardiac arrest in severe cases.

Greasewood (Sarcobatus Vermiculatus)

This shrub is common in alkaline soils, salt flats, and dry basins in western Colorado. It’s a problem for sheep in particular.

The plant accumulates oxalates, which can cause kidney damage and mineral imbalances when consumed in large quantities.

Identification: A spiny, gray-green shrub with small, fleshy leaves. It has inconspicuous flowers.
Symptoms in Animals: Symptoms include weakness, trembling, and recumbency due to low blood calcium levels.

How To Identify Poisonous Plants

Correct identification is your first line of defense. Never eat any wild plant unless you are 100% certain of its safety.

Key Visual Identification Features

Look for these common characteristics, but remember they are not definitive on their own.

Umbel Flowers: Many toxic plants in the carrot family (like hemlocks) have flowers in umbrella-like clusters.
Milky Sap: Some toxic plants exude a white, milky sap when broken (though not all plants with milky sap are poisonous).
Berries: Be very cautious of wild berries. Bright red and white berries are often warning colors in nature.
Thorns or Spines: While not always indicative of poison, they are a plant’s physical defense mechanism.

Using Field Guides And Apps

Invest in a good regional field guide. You can also use plant identification apps, but use them as a starting point, not a final authority.

Take clear photos of the entire plant, leaves, stems, and flowers.
Note the habitat: Is it wet, dry, sunny, or shaded?
Cross-reference with at least two reliable sources before making an identification for foraging purposes.

Common Look-Alikes And How To Tell Them Apart

Mistaking a toxic plant for an edible one is a common cause of poisoning.

Water Hemlock vs. Cow Parsnip or Celery

Water hemlock has smooth stems with purple streaks and its roots have a distinctive parsnip-like odor. Cow parsnip has large, hairy stems and no purple mottling.

Death Camas vs. Wild Onion or Camas

Crush a leaf. Death camas lacks the characteristic onion or garlic smell. True wild onions have a pungent, familiar odor.

Baneberry vs. Red Currant or Gooseberry

Baneberry berries grow on a single, thick red stalk. Currants and gooseberries grow in loose clusters directly from the stem.

What To Do In Case Of Exposure

Quick and correct action is crucial if you suspect poisoning. Do not wait for symptoms to appear.

For Human Exposure

Remove any plant material from the mouth.
Rinse the skin with soap and water if there was dermal contact.
Do not induce vomiting unless instructed by a professional.
Call the Poison Control Center immediately at 1-800-222-1222. They can provide specific, expert guidance.
Go to the nearest emergency room if advised, and if possible, bring a sample of the plant for identification.

For Pet Exposure

Prevent your pet from eating more of the plant.
Note the time of ingestion and try to identify the plant.
Contact your veterinarian or the ASPCA Animal Poison Control Center (888-426-4435) immediately. There is usually a fee for this service, but it is worth it.
Follow their instructions precisely. Do not give any home remedies unless directed.

For Livestock Exposure

Livestock poisoning often requires a different response due to the scale.

Remove animals from the pasture or area containing the toxic plant immediately.
Contact your local veterinarian or Colorado State University Extension office for assistance.
Provide plenty of fresh water and high-quality forage.
In some cases, veterinary intervention with activated charcoal or other treatments may be necessary.

Prevention and Safety Tips

Prevention is always better than treatment. Incorporate these habits into your outdoor routines.

For Hikers And Campers

Educate yourself and your children before you go. Show them pictures of the most dangerous plants.
Stay on designated trails to minimize contact with unknown vegetation.
Wear long pants and sleeves in areas with dense undergrowth.
Always supervise young children closely when they are playing in natural areas.

For Gardeners And Homeowners

Research the toxicity of any plant before adding it to your landscape, especially if you have pets or small children.
Consider removing highly toxic ornamentals like oleander if they pose a risk.
Wear gloves when handling plants you are unsure about, and wash your hands thoroughly afterward.

For Ranchers And Land Managers

Learn to identify the poisonous plants that are common in your region and pasture.
Manage grazing to avoid overuse, which can force animals to eat less desirable, potentially toxic plants.
Control the spread of invasive toxic plants like poison hemlock through mowing or approved herbicides at the correct time of year.
Provide adequate supplemental feed during drought conditions when forage is scarce.

Frequently Asked Questions

What Is The Most Dangerous Plant In Colorado?

Water hemlock (Cicuta species) is widely considered the most acutely toxic plant in Colorado. Ingesting even a small piece of the root can be fatal to a human or animal within hours due to severe seizures and respiratory failure.

Are Colorado’s Poisonous Plants A Risk In The Winter?

Yes, risk persists in winter. Some plants, like poison hemlock, retain dead stalks that still contain toxins. Others, like oleander as a houseplant, are present year-round. Livestock may also dig for roots of plants like water hemlock when other forage is buried under snow.

How Can I Tell If My Animal Has Eaten A Poisonous Plant?

Signs vary but often include sudden behavioral changes like depression or agitation, excessive drooling, difficulty breathing, tremors, stumbling, or collapse. If you notice any unusual symptoms and suspect plant poisoning, contact your vet immediately. Early intervention is critical.

What Should I Do If I Touch A Poisonous Plant Like Monkshood?

Wash the affected skin area immediately with soap and copious amounts of cool water. Remove any contaminated clothing. Monitor for symptoms like numbness or tingling. If symptoms develop, or if you have any concerns, contact Poison Control. The toxins can be absorbed through the skin.

Where Can I Get Help Identifying A Plant I Found?

You can contact your local Colorado State University Extension office. They have experts in plant identification. Many counties also have Master Gardener programs that can assist. Online, use reputable databases like those from universities or botanical gardens, not just general image searches.