''Toxicodendron rydbergii'', the western poison ivy, is a species of ''

Toxicodendron ''Toxicodendron'' is a genus of flowering plants in the sumac family, Anacardiaceae. It contains trees, shrubs and woody vines, including poison ivy, poison oak, and the lacquer tree. All members of the genus produce the skin-irritating oi ...

'' in the cashew family. It is native to most of

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

from the Maritimes to

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

, and most of the

contiguous Contiguity or contiguous may refer to: *Contiguous data storage, in computer science *Contiguity (probability theory) *Contiguity (psychology) *Contiguous distribution of species, in biogeography *Geographic contiguity of territorial land *Contigu ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

except the southeastern states,

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...

Delaware Delaware ( ) is a state in the Mid-Atlantic region of the United States, bordering Maryland to its south and west; Pennsylvania to its north; and New Jersey and the Atlantic Ocean to its east. The state takes its name from the adjacent Del ...

, and

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. It can be found growing in

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

s, and other wooded areas, usually near streams and

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...

s. Unlike ''

Toxicodendron radicans ''Toxicodendron radicans'', commonly known as eastern poison ivy or poison ivy, is an allergenic Asian and Eastern North American flowering plant in the genus ''Toxicodendron''. The species is well known for causing urushiol-induced contact derm ...

'' (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 Alternative or alternate may refer to: Arts, entertainment and media * Alternative (''Kamen Rider''), a character in the Japanese TV series ''Kamen Rider Ryuki'' * ''The Alternative'' (film), a 1978 Australian television film * ''The Alternative ...

. 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 Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struc ...

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 pre ...

, 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 Urushiol is an oily mixture of organic compounds with allergenic properties found in plants of the family Anacardiaceae, especially '' Toxicodendron'' ''spp.'' (e.g., poison oak, Chinese lacquer tree, poison ivy, poison sumac), ''Comoclad ...

, which can cause severe

contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are ...

in most individuals.

References

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