''Toxicodendron rydbergii'', the western poison ivy, is a species of '' Toxicodendron'' in the cashew family. It is native to most of

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from the

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, and most of the contiguous

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except the southeastern states,

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, and

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. It can be found growing in

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s, and other wooded areas, usually near streams and

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s. Unlike '' Toxicodendron radicans'' (eastern poison ivy), which often appears as a trailing or climbing vine, ''Toxicodendron rydbergii'' is a shrub that can grow to 1 m (3 ft) tall, rarely up to 3 m (10 ft). The leaves are

trifoliate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular ...

and alternate. The leaflets are variable in size and shape, and are usually 15 cm (6 in) long, turning yellow or orange in autumn. On the compound trifoliate leaves, the two leaflets opposite each other are typically

asymmetrical Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pr ...

, in contrast to the terminal leaflet which always shows bilateral symmetry. The fruits are small, round, and yellowish.Rydberg, Per Axel 1900. Memoirs of The New York Botanical Garden 1: 268–269
as ''Rhus rydbergii'' Poison Ivy Berries in the Wasatch Mountains

Poison Ivy Berries in the Wasatch Mountains

Description

'' Toxicodendron rydbergii '' is a bushy shrub (height 30 cm). Leaves alternate, often shiny; with 3 divisions (leaflets), each with a tail, the one in the center a little longer; leaflets irregular in outline and sinuous with or without teeth, well marked veins; color varying with the seasons: wine red in spring, green in summer and multicolored in autumn. Creamy white or greenish flowers clustered in cones at the base of the leaves. Ribbed fruits; white, yellow or brown; the size of a dry pea; noticeable especially when the leaves have fallen. Most often, we find individuals without flowers and fruits.

Caution

All parts of this plant contain urushiol, which can cause severe contact dermatitis in most individuals.

References

{{Taxonbar, from=Q7830405 rydbergii Flora of North America Plants described in 1900