Also known as Rydberg’s poison ivy, Canadian poison ivy, Northern poison ivy, Nonclimbing poison ivy;
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.
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).
Trunk and stems
Poison ivy is a woody plant, not herbaceous. Thus, when the three leaves are fallen, the trunk is like a twig persistent in autumn and winter, which can go up to 20 cm (8 in) from the ground in Northern US and Southern Canada. In regions with milder winters, the plant can become a small shrub that can reach three feet. The trunk and stem, like all parts of this plant, may cause skin irritation if broken and if the urushiol break out.
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. Often they remain throughout fall and winter on the main stem.
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. In the United States, aerial stems can stand milder winters and plant growth can continue in height and becoming a shrub. Suckering propagation becomes less important.
Habitat and distribution
Let’s start in the north. Western poison ivy is found in southern Canada, from the Fraser valley in B.C. to the Maritimes, with the exception of Newfoundland. As you move northward, the less you will have the opportunity to meet the plant. It seems that the western poison ivy can not stand harsh winter cold. By the way, no other toxicodendron can live in these regions. We now know where to take our next vacation.
In United-States, this plant is also widely present in the Rockies, from north to south, and up to the north-eastern states. The south-eastern states and the west coast are free of western poison ivy.
You can find western 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. Usually, very shady places, such as maple and dense forests, are less suitable for propagation.
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