western poison ivy

(Toxicodendron rydbergii)

Conservation Status

IUCN Red List

not listed

NatureServe

N5 - Secure

SNR - Unranked

Minnesota

not listed

 
western poison ivy
 
Weed Status

Specially Regulated Plant

In 2010, the Minnesota Department of Agriculture added eastern poison ivy and western poison ivy to the Specially Regulated Plant list.

Must be eradicated or controlled for public safety along rights-of-ways, trails, public accesses, business properties open to the public or on parts of lands where public access for business or commerce is granted. Must also be eradicated or controlled along property borders when requested by adjoining landowners.

Poison ivy is beneficial to many wildlife species, but exposure to it causes severe skin irritation to humans and sometimes to livestock. Smoke from burning it can cause serious respiratory problems.

Wetland Indicator Status

Great Plains

FACU - Facultative upland

Midwest

FAC - Facultative

Northcentral & Northeast

FAC - Facultative

Description

Western poison ivy is an erect, perennial shrub that rises on a single stem from a usually underground rhizome. It often forms colonies. The plant is usually a ground cover, sometimes a shrub, rarely a vine. If it is a vine it climbs weakly, and will not climb trees.

Stems are woody, erect, usually unbranched, and lack aerial roots.

Leaves are alternate and are borne near the end of the stem usually on leaf stalks. The leaf stalks are hairless and ½ to 10 long. The base of the leaf stem is enlarged and grooved. When the leaf is absent, a u-shaped or v-shaped scar remains.

The leaves are divided into 3 leaflets. The leaflets may be egg-shaped, with the broad portion at the base where it attaches to the leaf stalk, or diamond shaped, broadest in the middle and tapering toward both ends. They taper to a point at the tip. They are 1 to 6 long. The two side leaflets are usually shorter than the central leaflet. The leaflet margins may have shallow lobes, they may have rounded teeth, or they may be entire. They tend to be folded slightly along the midrib, not flat. The upper surface is usually entirely hairless, or there may be a line of curly hairs on the midvein. The lower surface is either entirely hairless or has appressed hairs. In the spring the leaves are glossy and have a reddish tint. Throughout the year young leaves are shiny becoming dull with maturity. In the fall the leaves turn yellow to orange, rarely bronze to red.

Black spots may appear on any part of the plant. The spots are urushiol, the resin that causes allergic reactions. When the plant is damaged urushiol is exuded in an attempt to seal off the damaged area. The resin is creamy, turning brown-red then black with oxidation.

The inflorescence is an elongated, 4 to 16 long, unbranched or sparingly branched cluster with usually fewer than 25 flowers. The flower has 5 yellowish petals.

The fruit is a hairless, greenish-white, berry-like pome that turns ivory at maturity. It is distinctly ridged, “like a pumpkin”. The fruit cluster is compact and erect.

 

Height

Up to 60 long

 

Flower Color

Yellowish

 

Similar Species

Boxelder (Acer negundo) saplings may have 3 (usually), 5 (occasionally), or 7 (rarely) leaflets. When it has 3 leaflets it can be indistinguishable from western poison ivy.

Eastern poison ivy (Toxicodendron radicans ssp. negundo) is a vine, not a shrub. It climbs trees. The stems have aerial roots. The leaf stalks are densely hairy. The leaflets tend to be flat, not folded along the midrib. The inflorescence is 3 to 4 long. The fruit cluster hangs downward.

Habitat

Dry to moist. Wood edges, prairies, fences, beneath utility wires. Full shade to partial sun.

Ecology

Flowering

June to August

 

Pests and Diseases

 

 

Toxicity

The sap of this plant contains the allergenic urushiol. Urushiol is not a single chemical but a complex of five chemicals called alkylcatechols.

Several exposures to the substance may be necessary to impart sensitivity. Research has shown that 85% of all people will develop contact dermatitis after adequate exposure. It usually takes 12 to 48 hours for a rash to develop on a previously sensitized person. In some individuals, a single exposure will cause a reaction. In these individuals, the rash will develop in seven to ten days.

The lesions last 14 to 20 days. Rashes do not spread and are not contagious. Treatment can dry the blisters, reduce swelling, and relieve itching, but will not speed healing.

Contact with the outer surface on an undamaged plant should not cause an allergic reaction unless there is residual urushiol present from a previous injury to the plant or a nearby plant. Contact with a torn leaf, broken or damaged stem or rhizome, or black spot will cause a reaction in those sensitized to urushiol.

Use

 

Distribution

Distribution Map

 

Sources

2, 3, 4, 5, 7, 8, 22, 24, 28, 29, 30.

2/20/2023    
     

Nativity

Native

     

Occurrence

Common and widespread

Taxonomy

Kingdom

Plantae (green algae and land plants)

Subkingdom

Viridiplantae (green plants)

Infrakingdom

Streptophyta (land plants and green algae)

Superdivision

Embryophyta (land plants)

Division

Tracheophyta (vascular plants)

Subdivision

Spermatophytina (seed plants)

Class

Magnoliopsida (flowering plants)

Subclass

Rosidae

Superorder

Rosanae

Order

Sapindales (soapberries, cashews, mahoganies, and allies)

Family

Anacardiaceae (cashew)

Subfamily

Anacardioideae (cashews, sumacs, and allies)

Genus

Toxicodendron (poison ivies and oaks)

   

Subordinate Taxa

 

   

Synonyms

Rhus radicans var. rydbergii

Rhus radicans var. vulgaris

Rhus toxicodendron var. vulgaris

Toxicodendron desertorum

Toxicodendron radicans var. rydbergii

   

Common Names

northern poison-ivy

Rydberg’s poison-ivy

western poison ivy

western poison-ivy

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Glossary

Entire

Continuous; not toothed, notched, or lobed.

 

Pome

A fruit with a central seed bearing core enclosed in thick flesh, e.g., an apple or pear.

 

Rhizome

A horizontal, usually underground stem. It serves as a reproductive structure, producing roots below and shoots above at the nodes.

 

Urushiol

Collectively, the five chemicals (alkylcatechols) in the sap of Toxicodendrons that cause allergic reactions in humans.

Visitor Photos
 

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Luciearl

western poison ivy   western poison ivy
     
western poison ivy  

 

Nancy Falkum

Blooming Poison Ivy  

 

western poison ivy  

 

Dan W. Andree

Poison Ivy....

I wasn’t sure just what it was but I knelt down to tie a shoe and my knee must have been on some and I got a itchy rash on it. I just washed my knee area and put some stuff for itch on it and it eventually went away. Had also noticed a few small red spots on my ankles that itched. Guessing the same thing. I looked it up and it appears to be poison ivy. It was at Frenchman’s Bluff SNA and seems to be in several different areas throughout that SNA. I have encountered other areas in some woodlands even certain weeds can cause itching. I have actually become immune to some types. The poison ivy irritation didn’t last that long and didn’t spread to any place else thankfully. But probably differs with each individual. I’ll be more careful where I kneel down to tie a shoe when out and about in certain areas.

 

western poison ivy

Scott Bemman

western poison ivy  

 

Wander Without Wifi

western poison ivy   western poison ivy

Bill Reynolds

western poison ivy   western poison ivy
MinnesotaSeasons.com Photos

Colony

western poison ivy   western poison ivy
     

Plant

western poison ivy   western poison ivy
     
western poison ivy   western poison ivy
     

Inflorescence

western poison ivy   western poison ivy
     

Leaves

western poison ivy   western poison ivy
     
western poison ivy    
     

Black Spots (Urushiol)

western poison ivy    
     

Aboveground Rhizome

western poison ivy    

 

Camera

Slideshows
Toxicodendron
Matt Lavin
Toxicodendron
About

Shrubs, subshrubs, and rarely vines that produce yellowish white drupes. Montana harbors only one species that is common along riparian corridors and on protected slopes with a south aspect.

 

slideshow

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Wander Without Wifi

SIBLEY STATE PARK - Minnesota. A PAINFUL FAIL!
Sep 11, 2020
About

We thought we were going to show you the natural wonders of Sibley State Park, a park that has been around for over 100 years. However, Mother Nature had other ideas. Please subscribe if you like what you see on Wander Without Wifi.

Other Videos
Blue Asters, Red Ivy
Carl Barrentine
About

Published on Sep 15, 2012

Blue big leaf asters (Eurybia macophylla?) and red western poison ivy (Toxicodendron rydbergii) make their seasonal contributions to our autumnal colors. Photographed at the Turtle River State Park, North Dakota (15 September 2012).

rhus toxicodendron
zebrablu
About

Uploaded on Aug 13, 2011

albero

 

Camcorder

Visitor Sightings
 

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Luciearl
2/20/2024

Location: Fairview Twp, Cass County

western poison ivy

Luciearl
1/31/2024

Location: Fairview Twp, Cass County

western poison ivy
Nancy Falkum
6/7/2015

Location: Kellogg Weaver Dunes SNA, Weaver Dunes Unit

Blooming Poison Ivy

western poison ivy
Scott Bemman
Summer 2020

Location: Frenchman’s Bluff SNA

I wasn’t sure just what it was but I knelt down to tie a shoe and my knee must have been on some and I got a itchy rash on it. I just washed my knee area and put some stuff for itch on it and it eventually went away. Had also noticed a few small red spots on my ankles that itched. Guessing the same thing. I looked it up and it appears to be poison ivy. It was at Frenchman’s Bluff SNA and seems to be in several different areas throughout that SNA. I have encountered other areas in some woodlands even certain weeds can cause itching. I have actually become immune to some types. The poison ivy irritation didn’t last that long and didn’t spread to any place else thankfully. But probably differs with each individual. I’ll be more careful where I kneel down to tie a shoe when out and about in certain areas.

western poison ivy
Scott Bemman
9/15/2020

Location: McCarthy Beach State Park

western poison ivy
Wander Without Wifi
9/15/2020

Location: McCarthy Beach State Park

western poison ivy
Bill Reynolds
6/1/2014

Location: Pennington Co MN

western poison ivy
Bill Reynolds
10/11/2013

Location: Pennington Co MN

western poison ivy
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