western poison ivy

(Toxicodendron rydbergii)

               
Conservation Status

IUCN Red List

not yet assessed

western poison ivy

NatureServe

N5 - Secure

SNR - Unranked

Minnesota

None
Wetland
Indicator
Status

Great Plains

FACU - Facultative Upland

Midwest

FAC - Facultative

Northcentral & Northeast

FAC - Facultative

Nativity

Native

Occurrence

Common and widespread

Habitat

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

Flowering

June to August

     
Flower Color

Yellowish

     
Height

Up to 60 long

     

Identification

This is an erect, perennial shrub that rises on a single stem from a usually underground rhizome. It often forms colonies. The plant form is variable. It plant can be either a shrub or, rarely, a vine. If it is a vine it climbs weakly, and will not climb trees. In Minnesota it often appears as a ground cover.

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 green berry that turns ivory at maturity. The fruit cluster is compact and erect.

 
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.


Distribution Range Map   Sources: 2, 3, 4, 5, 7, 8, 28.

Comments

Urushiol
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.


Taxonomy

Family:

Anacardiaceae (sumac)

 

Subfamily:

Anacardioideae

 
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.

 

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.

       

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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
       

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    
       
       
     

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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

 
     

 

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