(Toxicodendron rydbergii)
Conservation • Weed • Wetland • Description • Habitat • Biology • Use • Distribution • Taxonomy
Description |
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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 green berry that turns ivory at maturity. The fruit cluster is compact and erect. |
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Height |
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Up to 60′ long |
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Flower Color |
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Yellowish |
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Similar Species |
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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. |
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Habitat |
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Dry to moist. Wood edges, prairies, fences, beneath utility wires. Full shade to partial sun. |
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Biology |
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Flowering |
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June to August |
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Pests and Diseases |
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Toxicity |
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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. |
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Use |
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Distribution |
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Sources |
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2/20/2023 | ||||
Nativity |
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Native |
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Occurrence |
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Common and widespread |
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Taxonomy |
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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 |
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Synonyms |
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Rhus radicans var. rydbergii Rhus radicans var. vulgaris Rhus toxicodendron var. vulgaris Toxicodendron desertorum Toxicodendron radicans var. rydbergii |
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Common Names |
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northern poison-ivy Rydberg’s poison-ivy western poison ivy western poison-ivy |
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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.
Visitor Photos |
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Nancy Falkum |
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Blooming Poison Ivy |
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Dan W. Andree |
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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. |
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Scott Bemman |
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Wander Without Wifi |
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Bill Reynolds |
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MinnesotaSeasons.com Photos |
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Colony |
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Plant |
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Inflorescence |
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Leaves |
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Black Spots (Urushiol) |
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Aboveground Rhizome |
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Slideshows |
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Toxicodendron Matt Lavin |
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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. |
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Wander Without Wifi |
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SIBLEY STATE PARK - Minnesota. A PAINFUL FAIL! Sep 11, 2020 |
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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. |
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Other Videos |
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Blue Asters, Red Ivy Carl Barrentine |
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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). |
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rhus toxicodendron zebrablu |
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About
Uploaded on Aug 13, 2011 albero |
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Visitor Sightings |
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This button not working for you? Simply email us at info@MinnesotaSeasons.com. Be sure to include a location. |
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Nancy Falkum 6/7/2015 |
Location: Kellogg Weaver Dunes SNA, Weaver Dunes Unit Blooming Poison Ivy |
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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. |
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Scott Bemman 9/15/2020 |
Location: McCarthy Beach State Park |
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Wander Without Wifi 9/15/2020 |
Location: McCarthy Beach State Park |
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Bill Reynolds 6/1/2014 |
Location: Pennington Co MN |
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Bill Reynolds 10/11/2013 |
Location: Pennington Co MN |
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MinnesotaSeasons.com Sightings |
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Avon Hills Forest SNA, North Unit Bertram Chain of Lakes Regional Park Carpenter St. Croix Valley Nature Center Carver Highlands WMA, South Unit Charles A. Lindbergh State Park Clifton E. French Regional Park Hardscrabble Woods / MG Tusler Sanctuary Itasca Wilderness Sanctuary SNA John Peter Hoffman Spring Brook Valley WMA Kellogg Weaver Dunes SNA, Kellogg Weaver Unit Lake Alexander Woods SNA, South Unit Mary Schmidt Crawford Woods SNA Minnesota Valley NWR, Louisville Swamp Unit Minnesota Valley NWR, Wilkie Unit Mound Spring Prairie SNA, North Unit Nerstrand Big Woods State Park Northern Tallgrass Prairie NWR, Hoffman Unit Northern Tallgrass Prairie NWR, Rengstorf Unit Prairie Creek WMA, Koester Prairie Unit Robert Ney Memorial Park Reserve Sand Prairie Wildlife Management and Environmental Education Area Two Rivers Aspen Prairie Parkland SNA |
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