Western Poison Ivy, Western Poison-ivy: Toxicodendron rydbergii (Synonyms: Rhus radicans, Rhus radicans var. rydbergii, Rhus radicans var. vulgaris, Rhus rydbergii, Rhus toxicodendron var. vulgaris, Toxicodendron desertorum, Toxicodendron radicans)

Western poison ivy as seen along the trail that follows the north bank of the Little Spokane River from the Painted Rocks Trailhead.......May 7, 2012.

The genus name, Toxicodendron literally means from the Latin: toxico = poison and dendros = tree.

Poison ivy or poison oak is a rhizomatous shrub up to 1.5 meters tall. The stems are more or less erect and simple to sparingly branched. The herbage of the stems is pubescent, while the leaves are often glabrous on both surfaces, or occasionally hairy below with some hairs along the midrib above. Leaves are trifoliate with elongated petioles. Individual leaflets are ovate to broadly ovate or suborbicular. They range from 5-12 cm long with entire margins (occasionally with some irregular, pointed teeth. The tips of the leaves are acutely pointed or acuminate. The leaves are often folded upwards along the midrib as seen in the photos.

The axillary inflorescence is usually racemose with at most 25 flowers, or occasionally branched or paniculate with many flowers. The whitish flowers range from 2-3 mm long. The flowers are either male or female. Male flowers contain 5 fertile stamens. Female flowers contain 5-10 vestigial stamens separated from the ovary by a flat, lobed and fleshy disk. The style is short and 3-parted. The fruits are tiny white berries with a greenish or yellowish cast.

This plant contains oils which cause a severe dermatitis on many persons. Contact with any part of the plant, dead or alive may cause the allergic reaction.

Western poison ivy may be found in open, sunny areas. It is often found in rocky canyons or along streams in the valleys and foothills.

Western poison ivy may be found over much of the United States. It is found mostly in our area to the east of the Cascade Mts. It may be found from eastern Washington and Oregon east to the Atlantic Ocean and south to Mexico.

Western poison ivy as seen along the trail that follows the north bank of the Little Spokane River from the Painted Rocks Trailhead........May 7, 2012.

Western poison ivy growing at left along the John Day River at the junction of US Highway 26 and Oregon Highway 19, Grant County, Oregon........June 2, 2011. The photo at right shows western poison ivy growing along the Holland Falls National Recreation Trail #416, Flathead National Forest......May 27, 2023.

Western poison ivy growing along southern Douglas Creek, Douglas County, Washington..........June 3, 2013.

Western poison ivy from Horsethief Butte, Columbia River Gorge.........May 5, 2001.