Wildflowers of the United States

Western Poison Ivy, Northern Poison Ivy - Toxicodendron rydbergii

Family: Anacardiaceae - Cashew or Sumac family

Genus Common Name: Poison Oak

Native Status: Native

Dicot Perennial Shrub Herb Subshrub Vine

Toxicodendron rydbergii - Western Poison Ivy, Northern Poison Ivy. The genus Toxicodendron has 5 species native to the United States- two poison oaks, two poison ivys, and poison sumac. All produce oils which are a significant skin irritant to most people. The oil seems to be harmful only to humans, but animals who have come into contact with the plant may carry the oil to their human companions - watch out where your dog has been rolling.

While it is usually called Western Poison Ivy, it grows throughout southern Canada and the lower 48 United States, except in California and several southeastern states. In the eastern parts of the country it may be known by the common name Northern Poison Ivy.

It is classified as Endangered in Ohio.

Found in:
AZ, CO, CT, IA, ID, IL, IN, KS, MA, MD, ME, MI, MN, MT, NC, ND, NE, NH, NM, NV, NY, OH, OK, OR, PA, RI, SD, TX, UT, VA, VT, WA, WI, WV, WY

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Distribution of Toxicodendron rydbergii in the United States and Canada:

Map courtesy of The Biota of North America Program.
Map color key
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Site: Kleinschmidt Grade, Adams County, ID Date: 2012-May-25	Photographer: Gerald C. Williamson Nikon D7000
Western Poison Ivy blooms from late spring through early summer, and in some parts of the country may bloom a second time in late summer. The flowers are quite small and if you get close enough to enjoy them you risk contact and the adverse consequences.

Site: Kleinschmidt Grade, Adams County, ID Date: 2012-May-25	Photographer: Gerald C Williamson Nikon D7000
Western Poison Ivy is a normally a woody-stemmed shrub that may grow up to about 4 feet tall. While it may also sometimes show up as a vine, unlike Toxicodendron radicans (Eastern Poison Ivy) it does not climb extensively.
Click on the photo for a larger image
Site: Kleinschmidt Grade, Adams County, ID Date: 2012-May-25	Photographer: Gerald C Williamson Nikon D7000
The fruit of Toxicodendron rydbergii are eaten by some birds. Animals do not appear to have ill effect from the urushiol - the oil that causes allergic reaction in most humans. Urushiol is present in all plant parts, and is the same oil in all Toxicodendron species.
Click on the photo for a larger image
Site: Kleinschmidt Grade, Adams County, ID Date: 2012-May-25	Photographer: Gerald C Williamson Nikon D7000
The young leaves of Western Poison Ivy have a waxy appearance. While other plants also have three-part leaves, the "leaves of three, let it be" saying is worth teaching to your children.
Click on the photo for a larger image

References used for identification and information:

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Toxicodendron rydbergii initially published on USWildflowers.com 2012-08-11; Updated 2015-06-24

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2024
Photographs Copyright owned by the named photographer

Code Update 20230302