POISON IVIES: Eastern poison ivy and Western poison ivy

Eastern Poison Ivy,
Also known as Central poison ivy or Climbing poison ivy;
Toxicodendron Radicans

Often called only Poison ivy, its botanical name is Toxicodendron radicans. Six subspecies of the T. radicans exist (divaricatum, eximium, negundo, pubens, radicans, verrucosum) but I will not dwell on these subjects. Discovered by the first settlers, Eastern poison ivy is present in the eastern United States. This species of toxicodendron generates fine aerial roots that allow the plant to cling to the bark of trees and rise up to the top of them. That’s the major difference between Eastern and Western poison ivy. Also, “radicans” means “having rooting stems.” The Eastern poison ivy can be a climbing or crawling vine or be a shrub. The Western poison ivy (Rydberg) only crawls. Some still consider the Western poison ivy as a subspecies of the Eastern poison ivy.

Eastern Poison Ivy (Toxicodendron radicans) climbing on a tree. Copyright http://weedscanada.ca/cashew.html

Leaves

The saying “Leaves of three, let it be. Leaves of five let it thrive.” teaches us to beware of a plant that has three leaves. That is the case with the two poison ivies, and the two poison oaks. The leaf is a group of three leaflets at the end of a stem (petiole), which links the trunk. The central leaflet, pointing outward, has a longer stalk than the two others. The leaflets are egg-shaped ending in a point. The edges can be smooth, toothed or wavy. The leaves length can also vary greatly depending on the maturity of the plant, the soil type and the region. The leaves have a glossy (polished appearance) reddish in spring, green in summer and take different shades of yellow, orange, red or bronze in the fall.

Smooth poison ivy leaves

Nonclimbing and climbing Eastern poison ivy: 3 leaves with smooth edges.

Toothed poison ivy leaves

Eastern climbing poison ivy (T. radicans) can have toothed leaves.

Smooth poison ivy leaves in autumn

Climbing Eastern poison ivy (T. radicans) at fall with red leaves. Copyright http://weedscanada.ca/cashew.html

Trunk and stems

Climbing poison ivy (T. radicans) with earial rootlets on a tree. Closely.

Eastern poison ivy is a woody plant that climbs on trees, posts and anything vertical. Eastern poison ivy is a vine that goes up and, sometimes, a shrub. We can easily recognize the climbing Eastern poison ivy by the fine aerial roots that allow the plant to cling to the bark of trees. With all these fine roots, the trunk can sometimes look like a tousled old rope. The texture of the trunk is always slick with a grey-brown color. As the plant become stronger and the trunk wider, the plant can spread laterally to 8 feet or more from the trunk to reach sunlight. The trunk and stem, like all parts of this plant may cause skin irritation if broken and if the urushiol break out.

Climbing poison ivy (T. radicans) with aerial rootlets.
Copyright http://weedscanada.ca/cashew.html

The poison ivy shrub, a variant

The Toxicodendron radicans subsp. negundo also named Toxicodendron negundo is the shrub variant of the Eastern poison ivy. It doesn’t climb on the trees but grows as a small tree. It is also possible to see the little aerial rootlest on the branches.

Flowers and fruits

In June and July, some plants produce beige to yellow-green discrete flowers. These flowers are sometimes hidden by the leaves and hard to see. In late spring, beige round fruits with 1/8 to 1/4 in (3-7 mm) diameter, appear in clusters.

Propagation

This vigorous plant is propagated by its seeds, located within fruit. The fruit can drop near the plant or birds can eat the fruit and expel the seeds later in their droppings. Another plant can then push in this place, if the germination is done correctly. The poison ivy also spreads by suckering from its long root system located at the surface or just below the ground.

Poison ivy (Toxicodendron radicans) drawing.

Habitat and distribution

Eastern poison ivy is present in the eastern half of United States, up to the southern Ontario, Canada. If this variety of poison ivy is absent north of these regions is because its long aerial stems cannot withstand harsh winters.

You can find eastern poison ivy in various types of soils, in sunny or partial shade, wetlands, dry, sandy or rocky, on the edge of fields, roads, railways, rivers. The place where the plant is established is often densely settled and is spreading rapidly in deforested and disturbed lands. This plant can grow well where many other plants can not, such as dry, rocky and acid soils. Always keep your eyes open.

Climbing poison ivy habitat area (toxicodendron radicans).

Videos about Eastern poison ivy

How to identify poison ivy and stay away!

Poison Ivy and Poison Vine/Oak Identification

Facts about poison ivy and how to correctly identify poison ivy, poison oak and poison sumac.

Best Poison Ivy Video Identification Guide

Resources about Eastern poison ivy

Western poison ivy:
Also known as Rydberg’s poison ivy, Canadian poison ivy, Northern poison ivy, Nonclimbing poison ivy;
Toxicodendron Rydbergii

The botanical name of western poison ivy is Toxicodendron Rydbergii, but let’s shed a little light on their names. Western poison ivy and Eastern poison ivy have long been known and named as rhus radicans, then toxicodendron radicans, considering that it was one plant with two behaviors. Later, botany decided to separate the two variants: toxicodendron rydbergii for the creeping variety (on the ground) that sometimes appears as a shrub; toxicodendron radicans for climbing variety (in height). However, some botanists still disagree with this division. Often, the printing and web literature on the subject still brings together both types of poison ivy under the same term toxicodendron radicans and the mistake recurs over the years. Even Wikipedia and some documents from departments continue in this same old habit. In addition, in regions where both plants are present, hybridization between them can make it difficult to identify the plant.

Nonclimbing poison ivy (T. rydbergii) on a rocky area. Copyright http://weedscanada.ca/cashew.html

Leaf

The saying “Leaves of three, let it be. Leaves of five let it thrive.” teaches us to beware of a plant that has three leaves. That is the case with the two poison ivies, and the two poison oaks. The leaf is a group of three leaflets at the end of a stem (petiole), which links the trunk. The central leaflet, pointing outward, has a longer stalk than the two others. The leaflets are egg-shaped ending in a point. The edges can be smooth, toothed or wavy. The leaves length can also vary greatly depending on the maturity of the plant, the soil type and the region. The leaves have a glossy (polished appearance) reddish in spring, green in summer and take different shades of yellow, orange, red or bronze in the fall. The leaves are the highest part of the plant and can rise up to 20 in (50 cm) from the ground in sunny and suitable locations. In warmer regions, such as the eastern United States, western poison ivy can be a small shrub that can reach 3 feet (1 meter).

Western poison ivy (T. Rydbergii) can hav toothed leaves.

Nonclimbing poison ivy (T. rydbergii) between a forest and a field.