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  • Paul Frysh

Guide to Poisonous Plants

Poison Ivy

Like its cousins poison oak and poison sumac, it has an oily sap in its leaves called urushiol. This causes an allergic reaction that can make your skin red, swollen, and itchy. It grows over most of the U.S. except Alaska and Hawaii. Each stem grows into three “leaflets” that might help you notice it in the woods. In the East, Midwest, and South, it grows as a vine, and in the North and the West as a shrub.

Poison Oak

It looks a lot like poison ivy, but its leaves are more similar to those of an oak tree. The sun-facing side of the leaf has tiny hairs on it and is a darker shade of green than the ground-facing side. Though it grows all over the country, it’s more common in the West. It could be hours or days before your skin reacts to the plant sap (urushiol). And your rash may eventually turn bumpy and form blisters that ooze.

Poison Sumac

This woody shrub grows in wet, swampy areas all over the U.S. Each stem has 7 to 13 leaves and clusters of green berries that droop. Cool showers and calamine lotion might help relieve the itch, but mostly, you wait: A week or two should bring relief. See your doctor if the rash is on your face or private parts, covers more than 25% of your body, you notice pus from the rash, or you breathe in smoke from burning leaves.

Giant Hogweed

It lives in the rich, wet soil near ditches, streams, and farms, especially in the Northeast. It has umbrella-shaped groups of small white flowers, leaves with deep creases, and stems with white hairs and purple splotches. It grows as tall as 15 feet. Its sap can make your skin more sensitive to ultraviolet light, which could blister, burn, or scar it, sometimes permanently. It could even damage your vision.

Stinging Nettle

The little hairs on the stems of stinging nettle can inject your skin with a combination of chemicals. One of these, formic acid, helps put the “sting” in bee stings and fire ant bites. It’s part of what causes the itchy and even painful allergic skin reaction. Stems grow unbranched in patches to about 4 feet tall, but sometimes as high as 6 feet. Look for those stinging hairs on the stem, which are the telltale sign.

Australian Stinging Tree

While the American and European versions are safe, scientists have found a new neurotoxin in the Australian dendrocnide tree that can cause pain for days or even weeks. Tiny, fuzzy, needle-like growths called trichomes inject the poison, which is similar to that found in spiders and cone snails. Researchers named the new family of toxins gympeptides, after the tree’s local name, the Gympie-Gympie stinging tree.

Wild Parsnip

Coarse, saw-toothed leaves grow on hairy, grooved stems that are 2 to 5 feet tall. The yellow flowers grow in an umbrella pattern like other plants in the carrot family. When juice from crushed leaves, stalks, or flowers touches your skin, sunlight can cause a skin rash within a day or two. Look for the distinctive yellow flower in fields, roadsides, pastures, and Midwestern prairie.

Poison Hemlock

This plant looks like a wild carrot or an unusually big parsley plant because of the umbrella-like bunches of tiny white flowers and distinctive leaves. But it might be poison hemlock if you see purple blotches on the stem, a ridged fruit, or if it grows especially big (3 to 7 feet tall). It also has separated leaves that look similar to parsley.  It can poison humans and livestock when eaten. You could also get sick if you absorb plant oils through your skin.


People grow it for its looks throughout the United States. It thrives in the wild in some places, too. Its bell-shaped flowers are often bright purple but can be white, yellow, or pink. It blooms in the spring. It also has a fruit with lots of seeds, which kids sometimes eat. All parts of the flower are poisonous and can slow or disrupt your heart.

Bitter Nightshade

This woody perennial has a stem that grows through the year. It can reach up to 6 feet. Purple flowers in groups of three or more bloom around July or August. Kids are sometimes drawn to the roundish, juicy, glossy, red, poisonous berries. The poison (solanine) can give you headache, drowsiness, stomachache, vomiting, trembling, lowered temperature, dilated pupils, and diarrhea. If you think someone’s eaten it, get them to a doctor right away.


This strong-smelling nightshade herb has thick stems that grow 4 feet tall, with leaves up to 3 inches long. Nectar from the white, trumpet-shaped flower could make you sick, along with the leaves, and even the seeds, which some people use to get high. It makes you nauseous, thirsty, and feverish, weakens your pulse, and raises your heart rate. You might even forget where you are or see things that aren’t there.


This plant lives off of other trees and shrubs, which makes it a parasite. Its stems are thick and easy to break, with lots of branches. The leaves are often thick and stay green all year. Its little yellowish flowers don’t have petals. The small, white berries have one seed and contain a sticky, poisonous pulp. Keep this common Christmas holiday tradition away from kids and pets. The berries can give you diarrhea and slow or stop your heart.


This tall shrub has long, leathery leaves that grow in groups of three. Bright clusters of flowers bloom at the ends of branches in colors that vary from red and pink to white. All parts of the plant are very poisonous. Just one leaf is enough to kill an adult. You may have serious stomach pain, diarrhea, vomiting, dilated pupils, dizziness, and breathing problems.

Azalea and Rhododendron

Roman soldiers got sick on “mad honey” made from these flowers in the first century BCE. Historians think their enemies in Turkey gave it to them to weaken them before battle. It worked: The Romans lost. The leaves, nectar, and flowers of these bushes can poison you too, though you’d need to eat a lot. It irritates the mouth and could make you nauseated enough to vomit. Kids may mistake it for honeysuckle and eat the nectar.

If You Suspect Poison

Act fast. Call 911 if someone has a seizure, has trouble breathing, or loses consciousness. If your throat or mouth feels burned or irritated, try to drink a little milk or water. Get away from any suspected toxic fumes and into the fresh air. If the poison got onto your skin, rinse it quickly. If it got into your eyes, rinse them with saline drops if you can. Keep it up for 15 to 20 minutes. Call poison control as soon as possible for instructions about specific poisons.


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