Identifying Northwest Trees that Have Leaves Poisonous for Humans

Spending time in nature is one of the best feelings in the world. It gives you a chance to get out of your daily worries and feeds your soul. However, nature can be as dangerous as it can be beautiful and healing.

Plants can be poisonous in two ways: when they are touched and when they are ingested. Whether you are hiking or tending your own lawn, you should be aware of the poisonous plants that may be disguised as harmless, lovely, or mouthwatering plants. Poisonous plants can be more than just uncomfortable—they can be dangerous.

Here are a few tips to help you identify plants that have poisonous leaves for humans when you’re out in the wild or in your own yard:

Poison Ivy

Identifying Northwest Trees that Have Leaves Poisonous for Humans - poison ivy

Poison ivy is the most common poisonous plant in the northwestern USA. Despite being called ivy, it is not a true ivy, as it doesn’t always climb. Due to the variability in its appearance and habitat, it can be found as a shrub or a vine. A clear liquid compound called urushiol is found in its sap, and this causes the itchy reaction when poison ivy is touched. Although most animals are immune to poison ivy’s effects, its leaves are poisonous for 80 percent of the human population.

Poison ivy can be identified by its leaf structure. Its leaves grow in clusters of three leaves, with two opposing leaves and one central leaf. The adage, “Leaves in three, let it be!” is meant to identify poison ivy. Each three-leaf cluster grows on a stem that connects to the main vine. So if every single leaf is actually three leaflets growing off the main leaf stem growing off a branch, you should leave it alone.

Another marker for poison ivy plants is their alternating features. Their leaf stems alternate on the branch, never directly opposing each other. Similarly, the flowers on the branches and the veins on the leaflets are also alternating and never directly opposing each other.

Beware that this plant is poisonous even in dormancy, when it sheds its leaves.

Poison Oak

Identifying Northwest Trees that Have Leaves Poisonous for Humans - poison oak

Despite its name, poison oak is not a type of oak tree, but rather a vine or shrub that is extremely common in the northwestern USA. While it’s not a tree, its vines often grow on and around trees, so be careful of its presence around strange trees.

Poison oak contains the oil urushiol on its leaves and twigs, which is what causes the irritating reaction on most people. Poison oak can be recognized by its compound leaves of three leaflets each, just like poison ivy. However, unlike poison ivy, poison oak has distinctive scalloped leaflets, which gives them the look of oak leaves. These leaves are brighter on top and slightly hairy at the bottom. During spring, poison oak also sprouts white flowers.

Poison oak is similar to poison ivy in that both follow the, “Leaves in three, let it be!” rule, and the alternating features rule applies to poison oak as well.

Poison Sumac

Poison sumac is a small tree with a few wide-spreading branches and is generally found around swamps and marshes. Similar to poison ivy and poison oak, this plant also produces the oily allergen called urushiol, which causes painful rashes on humans. Its compound leaves are pinnate, containing an odd number of leaflets, usually between 7 and 13. These leaflets are 2 to 4 inches long with smooth edges and a pointed tip. As this plant grows quite tall, it tends to affect the faces and heads of humans.

Stinging Nettle

Identifying Northwest Trees that Have Leaves Poisonous for Humans - stinging nettles

Stinging nettle is a common northwestern perennial shrub that grows to about 2 to 4 feet tall. It produces small whitish flowers in the summer. Its leaves are heart-shaped, finely toothed, and tapered at the ends.

Stinging nettle plants are very hairy on the underside of the leaves and stems. These small, hair-like needles turn its leaves poisonous for humans and cause painful rashes and itching when touched.

The young leaves on these plants are high in calcium, iron, vitamin A, and vitamin C, and can generally be consumed after cooking. Cooking deactivates their poison and allows humans to enjoy its medicinal benefits harmlessly. As with any wild plant, however, consult an herbal specialist or your doctor before ingesting.


Identifying Northwest Trees that Have Leaves Poisonous for Humans - oleander

Oleander is an extremely toxic ornamental shrub that is prized by gardeners for its beautiful flowers and its ease of maintenance.

However, oleander contains several toxic elements, including cardiac glycosides, saponins, digitoxigenin, oleandrin, oleondroside, nerioside, and other unknown toxins, spread out in all parts of the oleander plant. This makes the plant dangerous, whether its parts are dried or green.

Signs of poisoning appear quickly and include severe vomiting and diarrhea, swollen and inflamed oral tissues, cold extremities, dilated pupils, increased heart rate, weakness, and death. Food that has touched oleander turns toxic, as does smoke made by burning oleander. Be very careful while handling this plant, and make sure not to directly touch your eyes or mouth after touching it.

If you do get exposed to any such poisonous plants, you may notice your skin becoming itchy or red. These rashes or irritations generally don’t spread by scratching. However, the residue of the plants’ poison might still be on your skin. So at the first sign of irritation, wash your hands and any skin that might have come in contact with the plant with soap and water and gently blot dry. Avoid touching your eyes and mouth. Consult your doctor if the rash worsens or if you develop blisters.

The best way to identify trees that have poisonous leaves for humans is to become familiar with pictures of common varieties of plants growing in your area and to keep an eye out for all kinds of new plants sprouting around you. In most cases, avoiding these poisonous plants is relatively easy, but you might notice some of these varieties growing on your property.

One thing to remember is that you should never try to get rid of a poisonous plant by burning it. This might vaporize the poison contained in the plant and be toxic to the lungs if inhaled. In these cases, you can reach out to professional arborists, such as Mr. Tree, to have any such toxic plants removed from your property.

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