Carnegiea gigantea, Giant Saguaro

Southwest Desert Flora

Home to the plants of the Sonoran, Chihuahuan and Mojave Deserts

Cirsium ochrocentrum, Yellowspine Thistle

Toxicodendron rydbergii, Western Poison Ivy

Western Poison Ivy has small white or white-greenish flowers on a loose flowering stalk and the flowers do not appear until the leaves have developed. Toxicodendron rydbergii Western Poison Ivy green shiny trifoliate leaves and the middle leaflet is long stalked; the leaflets are oblong-lanceolate to ovate and may grow up to 4 inches long. Toxicodendron rydbergii Western Poison Ivy is found throughout much of the United States and Canada. Western Poison Ivy, at least in its preferred western habitats, is not a predominant species. However eastern North American species, and certainly Eastern Poison Ivy are most often predominant species where found. Toxicodendron rydbergii Western Poison Ivy is a native perennial that blooms from April to September and prefers habitats in elevations from 3,000 to 8,000 feet. Toxicodendron rydbergii

Scientific Name: Toxicodendron rydbergii
Common Name: Western Poison Ivy

Also Called: Poison Ivy, Poison Oak

Family: Anacardiaceae, Sumac Family

Synonyms: (Rhus radicans var. rydbergii, Rhus toxicodendron radicans var. vulgaris, Toxicodendron crenatum, Toxicodendron desertorum, Toxicodendron radicans, Toxicodendron volubile)

Status: Native

Duration: Perennial

Size: Up to 3½ inches (8.9 cm) or so depending on growth form below.

Growth Form: Forb/herb, shrub, subshrub, vine; plants finely pubescent or nearly hairless; stems erect, ascending or climbing by areole rootlets.

Leaves: Green, shiny green, deciduous trifoliolate or trifoliate, middle leaflet long stalked (petiole); leaflets up to 4 inches (10 cm) long, oblong-lanceolate to ovate, often coarsely few-toothed.

Flower Color: White, greenish-white; inflorescence loose; paniculate, appearing after leaves develop; petals greenish-white.

Flowering Season: 3,000 to 8,000 feet (914-2,438 m).

Elevation: April to September

Habitat Preferences: In Arizona Western Poison Ivy is common in rich soil in ravines and canyons. In general, in the western United States, Western Poison-ivy most often occurs, but is seldom predominant, in gallery forests and floodplain communities.

Recorded Range: Wester Poison Ivy is found over most of North America, absent in several southeastern states and California.

North America & US County Distribution Map for Toxicodendron rydbergii.

U.S. Weed Information: In North America Toxicodendron rydbergii, Western Poison Ivy, can be weedy or invasive according to the following authoritative sources: Weeds of Nebraska and the Great Plains. Plants included here may become weedy or invasive.

Invasive/Noxious Weed Information: No information available.

Wetland Indicator: In North America Toxicodendron rydbergii has the following wetland designations:
Arid West, FACU;
Atlantic and Gulf Coastal Plain, FAC;
Eastern Mountains and Piedmont, FAC;
Great Plains, FACU; Midwest, FAC;
Northcentral & Northeast, FAC;
Western Mountains, Valleys, and Coast FACU.
FACU = Facultative Upland, usually occur in non-wetlands, but may occur in wetlands
FAC = Facultative, occur in wetlands and non-wetlands.

Threatened/Endangered Information: In North America Toxicodendron rydbergii, Northern Poison-ivy, is listed as "Endangered" by the state of Ohio.

Genus Information: In North America there are 7 species and 7 accepted taxa overall for Toxicodendron. Worldwide, The Plant List includes 30 accepted species names and a further 36 of infraspecific rank for the genus. The genus Toxicodendron was published by Philip Miller in 1754.

In the Southwestern United States: Arizona and Nevada each have 2 species of genus Toxicodendron, California, Utah and New Mexico each have 1 species and Texas has 4 species. All data is approximate and subject to taxonomic changes.

Comments: Western Poison Ivy is found throughout much of the United States and Canada and Western Poison Ivy, at least in its preferred western habitats, is not a predominant species. However Poison-ivies in the eastern United States, and certainly Eastern Poison Ivy, are most often predominant species where they are found.

Toxicodendron rydbergii contains a chemical that in some people causes painful swelling, rashes and eruptions of the outer-skin, thus the common name "Poison Ivy".

Importance to Wildlife, Birds and Livestock
Western Poison Ivy, and all Poison-ivies provide food for birds, small mammals, wild ungulates and livestock.

Mammals such as bears, mule deer, white-tailed deer, moose, foxes, woodchucks, muskrats, rabbits, squirrels, woodrats and mice consume the leaves, stems, and fruits of poison-ivies.

Livestock typically browse poison-ivies only sparsely however, heavy livestock usage may occur and may reduce the local abundance of the species.

Several species of birds, including gallinaceous birds such as wild turkeys, northern bobwhites, ruffed grouse and sharp-tailed grouse eat the fruits and seeds.

Special Value to Native Bees, Butterflies and Insects
No information available
The genus Toxicodendron means "poison tree". The genus Toxicodendron was published by Philip Miller in 1754.
The species epithet "rydbergii" is named in honor of Per Axel Rydberg (1860-1931). Mr. Rydbergii wrote the first book on the flora of the Rockies from Canada to Mexico, among other floras.
Toxicodendron rydbergii has been used for food as a blood medicine United States indigenous peoples.
  • Iroquois Drug, Blood Medicine, Poultice of plant applied to the skin as a vesicatory for water in the blood.
  • Lakota Drug, Poison, Poisonous plant caused a rash resembling venereal disease.

  • See complete listing of ethno-botanical uses at Native American Ethnobotany, University of Michigan, Dearborn.
    Date Profile Completed: 05/05/2017, updated 01/21/2020
    Arizona Flora, Kearney, Thomas H., Peebles, Robert H., 1960, University of California Press, Berkley and Los Angeles, California, as Rhus radicans var. rydbergii.
    U.S. Dept. of Agriculture, Natural Resources Conservation Service on-line database and USGS ITIS search - (accessed 01/21/2020)
    The Plant List (2013). Version 1.1. Published on the Internet; (accessed 01/21/2020).
    Innes, Robin J. 2012. Toxicodendron radicans, T. rydbergii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). [2020, January 21].
    Native Plant Information Network, NPIN (2013). Published on the Internet (accessed 01/21/2020). Lady Bird Johnson Wildflower Center at The University of Texas, Austin, TX.
    SEINet synonyms, scientific names, geographic locations, general information - (accessed ).
    ETYMOLOGY: Michael L. Charters; California Plant Names: Latin and Greek Meanings and Derivations; A Dictionary of Botanical and Biographical Etymology; (accessed 01/21/2020)