Photo by Melody

PlantFiles: Rydberg's Poison Ivy, Western Poison Ivy
Toxicodendron rydbergii

Family: Anacardiaceae (an-a-kard-ee-AY-see-ee) (Info)
Genus: Toxicodendron (toks-ee-ko-DEN-dron) (Info)
Species: rydbergii (ryd-BERG-ee-eye) (Info)

Synonym:Rhus radicans var. rydbergii
Synonym:Rhus radican var. vulgaris
Synonym:Rhus toxicodendron var. vulgaris
Synonym:Toxicodendron desertorum
Synonym:Toxicodendron radicans var. rydbergii

One member has or wants this plant for trade.

Vines and Climbers

6-8 ft. (1.8-2.4 m)

Unknown - Tell us

USDA Zone 3a: to -39.9 C (-40 F)
USDA Zone 3b: to -37.2 C (-35 F)
USDA Zone 4a: to -34.4 C (-30 F)
USDA Zone 4b: to -31.6 C (-25 F)
USDA Zone 5a: to -28.8 C (-20 F)
USDA Zone 5b: to -26.1 C (-15 F)
USDA Zone 6a: to -23.3 C (-10 F)
USDA Zone 6b: to -20.5 C (-5 F)
USDA Zone 7a: to -17.7 C (0 F)
USDA Zone 7b: to -14.9 C (5 F)
USDA Zone 8a: to -12.2 C (10 F)
USDA Zone 8b: to -9.4 C (15 F)
USDA Zone 9a: to -6.6 C (20 F)
USDA Zone 9b: to -3.8 C (25 F)
USDA Zone 10a: to -1.1 C (30 F)
USDA Zone 10b: to 1.7 C (35 F)

Sun Exposure:
Sun to Partial Shade

All parts of plant are poisonous if ingested
Handling plant may cause skin irritation or allergic reaction

Bloom Color:
White/Near White

Bloom Time:
Late Spring/Early Summer
Mid Summer
Late Summer/Early Fall

Good Fall Color

Other details:
May be a noxious weed or invasive

Soil pH requirements:
Unknown - Tell us

Patent Information:

Propagation Methods:
Unknown - Tell us

Seed Collecting:
Unknown - Tell us

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By kennedyh
Thumbnail #1 of Toxicodendron rydbergii by kennedyh

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By Malus2006
Thumbnail #5 of Toxicodendron rydbergii by Malus2006

By Malus2006
Thumbnail #6 of Toxicodendron rydbergii by Malus2006

By htop
Thumbnail #7 of Toxicodendron rydbergii by htop

There are a total of 9 photos.
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No positives
1 neutral
1 negative

Gardeners' Notes:

Negative ElecCham On Jun 7, 2010, ElecCham from Lafayette, CO wrote:

I've lived back and forth between Colorado and in Illinois for pretty much my whole life. From the Midwest, I was plenty familiar with poison ivy, and didn't seem to be affected by it. At camp one year, I'd tripped and fallen - right into a bed of the stuff. I showered off and washed my clothes, but apparently for others' benefit more than my own.

The previous house I lived in here in Colorado was very near Boulder Creek, right on the side of a hill. I was doing some gardening work... and then *later* learned about Western poison ivy. Apparently I am only immune to the Eastern variety...

Forget what you knew about how it looks, other than that it has three leaves; if the ones I had were any good example, the leaves are fairly light green, smooth, thin, and not glossy at all. Malus2006's comment regarding the shrub or sub-shrub forms is dead on - the ones in my yard all grew as a single stem with three leaves. Once the season progressed and the plants got bigger - the leaves grew to about 8" long! - they did begin to turn a bit red.

That was six months of hell; the steroidal anti-inflammatory I was prescribed listed "skin irritation" as a rare side-effect... and guess what? Before I put it together that it was not simply the original reaction getting worse, I had one night where I was seriously contemplating whether bashing my head in was a reasonable way to stop the itching. (Not managing to sleep in two days probably had something to do with that too. The doc prescribed me a straight antihistamine the next morning.) Even after it all cleared up, for the next six months I spent more time sick than I think I ever have, my immune system was so screwed up.

One more note: for the unfortunate soul who gets into this stuff, I made heavy use of the Aveeno oatmeal bath stuff. With the one night I mentioned before, in all seriousness, this possibly saved my life...

Neutral Malus2006 On Feb 9, 2009, Malus2006 from Coon Rapids, MN (Zone 4a) wrote:

This species of poison ivy is strongly shrub form - it never vines at all. In Minnesota where I live, I have never had seen vining form of poison ivy anywhere in the state. In shrub form, it is mainly a single wood stem, rarely branching. Most of the poison ivy I have seen tend to be less than one foot, making them look almost like they are "vining" along the ground when in reality they are rhizome through the ground, coming up in short wood stems. In certain favorable conditons, so far I have seen mainly floodplain habitation, they get tall - one was almost my height at five feet. In late fall to winter, their white berries atop their wood stems can look odd, especially in grassy areas. This species strongly favors woodland edges, and rarely go far deeper in the woodland. It can extend a good distance away from woodland edge, but it depends on how thick the grasses are - it won't surivive in open areas without some shrub or tree to thin out the grasses with their shade.

It doesn't care whenever the site it grows on are dry or moist - I have seen it grow on dry sandy soil and on rich floodplain soil.

A better common name is shrub poison ivy as it is also found in the northern part of East United States so Western Poison Ivy is not really a good name.

By Plant Profiles, the range of this species includes most of Western US, all of South Canada, and the northern part of East US down to Virginia.


This plant has been said to grow in the following regions:

Boulder, Colorado
Mackinaw, Illinois
Minneapolis, Minnesota
Hulbert, Oklahoma
Conway, South Carolina
Baytown, Texas
Celeste, Texas

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